[PROF-13115] Fix profiler support for Ruby 4.0.0-preview2

[ivoanjo]

What does this PR do?

This PR contains 3 small fixes for profiler support in Ruby 4.0.0-preview2:

1. rb_obj_info is not available in Ruby 4
2. Remove a pending from a spec that didn't work on Ruby 3.5.0-preview1
3. Stack trace behavior slightly changed in Ruby 4

It does not affect other Ruby versions.

Motivation:

This PR, together with #5090 and DataDog/datadog-ruby_core_source#18 is needed to get a green CI for the profiler on Ruby 4.

Change log entry

Yes. Fix profiler support for Ruby 4.0.0-preview2

Additional Notes:

N/A

How to test the change?

We don't yet have Ruby 4 in CI, so this can only be tested locally.

[datadog-official]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage
• Patch Coverage: 42.11%
• Total Coverage: 95.16% (-0.01%)

View detailed report

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[pr-commenter]

Benchmarks

Benchmark execution time: 2025-11-25 14:04:17

Comparing candidate commit 49e66f9 in PR branch ivoanjo/prof-13115-ruby-4_0_0-preview2-profiler with baseline commit 7084871 in branch master.

Found 2 performance improvements and 0 performance regressions! Performance is the same for 42 metrics, 2 unstable metrics.

scenario:error - error tracking, with_error=true - third_party only

• 🟩 throughput [+610.187op/s; +656.548op/s] or [+5.737%; +6.173%]

scenario:profiling - Allocations ()

• 🟩 throughput [+195862.641op/s; +203332.196op/s] or [+6.248%; +6.486%]

[lloeki]

LGTM