impl: new backend API

[arkjedrz]

• Backend implementation provided by DI.
• Built-in JsonBackend is now public.
• Added JsonBackendBuilder.
• Added docs/class_diagram.puml with current design.
• Updated tests and examples.

[Copilot]

Pull Request Overview

This PR refactors the KVS backend architecture to use dependency injection, making the backend implementation pluggable rather than hardcoded. The JsonBackend is now a public, configurable component with its own builder pattern.

Key changes:

• Introduced KvsBackend trait with methods for loading, saving, and managing snapshots
• Made JsonBackend public with JsonBackendBuilder for configuration
• Removed file path methods from KVS API (get_kvs_filename, get_hash_filename)
• Updated all tests and examples to use the new builder-based backend configuration

Reviewed Changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/rust/rust_kvs/src/lib.rs	Exposed backend modules and updated prelude exports
src/rust/rust_kvs/src/kvs_backend.rs	Defined KvsBackend trait with DynEq for dynamic equality checks
src/rust/rust_kvs/src/json_backend.rs	Made JsonBackend public, added builder, moved snapshot rotation logic
src/rust/rust_kvs/src/kvs_builder.rs	Refactored to accept backend via DI, simplified parameter handling
src/rust/rust_kvs/src/kvs.rs	Delegated backend operations to injected backend implementation
src/rust/rust_kvs/src/kvs_api.rs	Removed file path retrieval methods, added Eq derives
src/rust/rust_kvs/src/kvs_mock.rs	Removed mock implementations of deleted file path methods
src/rust/rust_kvs_tool/src/kvs_tool.rs	Added backend downcasting to access backend-specific methods
tests/rust_test_scenarios/src/helpers/mod.rs	Added helper for computing expected file paths
tests/rust_test_scenarios/src/helpers/kvs_instance.rs	Updated to build backend separately before passing to builder
tests/rust_test_scenarios/src/test_basic.rs	Simplified to use helper function
tests/rust_test_scenarios/src/cit/*.rs	Updated to use new helper and check file existence directly
tests/python_test_cases/tests/test_cit_snapshots.py	Updated assertions to check path strings and existence flags
src/rust/rust_kvs/examples/*.rs	Updated all examples to use new backend builder pattern
docs/class_diagram.puml	Added PlantUML class diagram documenting new architecture

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[github-actions]

License Check Results

🚀 The license check job ran with the Bazel command:

bazel run //:license-check

Status: ⚠️ Needs Review

Click to expand output

[License Check Output]
Extracting Bazel installation...
Starting local Bazel server (8.3.0) and connecting to it...
INFO: Invocation ID: 042c341f-dc66-4fae-9a31-4763b9964912
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
DEBUG: Rule 'rust_qnx8_toolchain+' indicated that a canonical reproducible form can be obtained by modifying arguments integrity = "sha256-oEubHgeZDdT0svMmBKJx7c3/2TdSI/vfwRUyDn+TPGA="
DEBUG: Repository rust_qnx8_toolchain+ instantiated at:
  <builtin>: in <toplevel>
Repository rule http_archive defined at:
  /home/runner/.bazel/external/bazel_tools/tools/build_defs/repo/http.bzl:394:31: in <toplevel>
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
WARNING: For repository 'rules_rust', the root module requires module version [email protected], but got [email protected] in the resolved dependency graph. Please update the version in your MODULE.bazel or set --check_direct_dependencies=off
WARNING: For repository 'rules_cc', the root module requires module version [email protected], but got [email protected] in the resolved dependency graph. Please update the version in your MODULE.bazel or set --check_direct_dependencies=off
WARNING: For repository 'platforms', the root module requires module version [email protected], but got [email protected] in the resolved dependency graph. Please update the version in your MODULE.bazel or set --check_direct_dependencies=off
Computing main repo mapping: 
Loading: 
Loading: 4 packages loaded
Loading: 4 packages loaded
    currently loading: 
Analyzing: target //:license-check (5 packages loaded, 0 targets configured)
Analyzing: target //:license-check (5 packages loaded, 0 targets configured)

Analyzing: target //:license-check (90 packages loaded, 9 targets configured)

Analyzing: target //:license-check (93 packages loaded, 10 targets configured)

Analyzing: target //:license-check (156 packages loaded, 5708 targets configured)

Analyzing: target //:license-check (162 packages loaded, 6985 targets configured)

INFO: Analyzed target //:license-check (165 packages loaded, 9001 targets configured).

INFO: From Generating Dash formatted dependency file ...:
INFO: Successfully converted 65 packages from Cargo.lock to bazel-out/k8-fastbuild/bin/formatted.txt
INFO: Found 1 target...
Target //:license.check.license_check up-to-date:
  bazel-bin/license.check.license_check
  bazel-bin/license.check.license_check.jar
INFO: Elapsed time: 31.156s, Critical Path: 0.37s
INFO: 14 processes: 5 disk cache hit, 9 internal.
INFO: Build completed successfully, 14 total actions
INFO: Running command line: bazel-bin/license.check.license_check ./formatted.txt <args omitted>
usage: org.eclipse.dash.licenses.cli.Main [-batch <int>] [-cd <url>]
       [-confidence <int>] [-ef <url>] [-excludeSources <sources>] [-help] [-lic
       <url>] [-project <shortname>] [-repo <url>] [-review] [-summary <file>]
       [-timeout <seconds>] [-token <token>]

[github-actions]

The created documentation from the pull request is available at: docu-html