Reorganize tests to tests/ directory for better E2E testing

[steph-rs]

Summary:

Move integration tests from src/tests/ to tests/ directory following rust conventions. Unit tests requiring private interfaces stay in src/.

Structure:

  crates/
  ├── metering/
  │   ├── src/
  │   │   ├── meter.rs         # Unit tests stay here (with #[cfg(test)])
  │   │   └── rpc.rs           # Unit tests stay here (with #[cfg(test)])
  │   └── tests/               # Integration tests (12 tests)
  │       ├── common/mod.rs
  │       ├── rpc.rs
  │       └── meter.rs
  └── flashblocks-rpc/
      ├── src/
      │   ├── state.rs         # Inline unit tests stay here
      │   └── ...              # Other modules keep their unit tests
      └── tests/               # Integration tests (24 tests)
          ├── common/mod.rs
          ├── rpc.rs
          └── state.rs

Benefits:

• Integration tests in separate crate - tests public API only, validates external interface
• Unit tests stay in src/ - still have access to private functions/types when needed
• Clear separation - integration/E2E in tests/, unit tests in src/
• Foundation for improve eth_call tests to have more real-world scenarios #151 - easy to add ERC-20, proxy contract, real-world scenario tests
• Standard Rust layout - easier for contributors to navigate

As the repo develops, new tests are required. I believe it's time for a clear division between the two types of tests, so it will be easier for new contributors to write new tests with the right approach.

[steph-rs]

@haardikk21 lmk what you think, please. I already did that, but changes looks huge because of the moved tests.

[haardikk21]

@haardikk21 lmk what you think, please. I already did that, but changes looks huge because of the moved tests.

Sounds good to me. Im going to create a new parent issue soon for a big tests refactor that can include this and a few other things I have in mind - as the current tests situation is, lets just say, not great.

[github-actions]

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