Streamline ddsketch loading, remove circular dependencies

[p-datadog]

What does this PR do?
Changes how ddsketch / libdatadog integration is handled:

Before, there was a lib/datadog/core/ddsketch.rb file which contained a class-level supported? method. Having this file meant that you could always require datadog/core/ddsketch, but you wouldn't always get a functional ddsketch out of that require.

The proposed change is to delete this file completely. Loading datadog/core will attempt to bring in ddsketch (and this is already behavior in master), therefore no additional require is needed for ddsketch.

To check for ddsketch presence, the supported? method was moved up to Datadog::Core module (up from Datadog::Core::DDSketch). Meaning:

1. if ddsketch is not supported, Datadog::Core::DDSketch will be not defined at all.
2. one does not need to require ddsketch to see if it's supported.

Motivation:
Removing circular dependency: ddsketch -> core -> configuration -> ddsketch

Change log entry
None

Additional Notes:

How to test the change?
Existing CI

[github-actions]

Thank you for updating Change log entry section 👏

^{Visited at: 2025-11-06 13:31:16 UTC}

[github-actions]

Typing analysis

This PR does not change typing compared to the base branch.

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-11-07 11:06:56

Comparing candidate commit 78bce97 in PR branch core-libdatadog-dep with baseline commit 4d6369e in branch master.

Found 0 performance improvements and 1 performance regressions! Performance is the same for 43 metrics, 2 unstable metrics.

scenario:profiling - gvl benchmark samples

• 🟥 throughput [-733.678op/s; -722.403op/s] or [-5.574%; -5.488%]

[datadog-official]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage
• Patch Coverage: 100.00%
• Total Coverage: 98.53% (-0.00%)

View detailed report

_{This comment will be updated automatically if new data arrives.
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[p-datadog]

CI is failing due to missing type declaration, I'll add it if there is consensus that this change is the way to go.

[ivoanjo]

👍 So I think this change is fine, but I'm curious -- where is the circular dependency again?

You listed

Removing circular dependency: ddsketch -> core -> configuration -> ddsketch

But... lib/datadog/core/ddsketch.rb did not require anything before, so I'm not sure where the circular dependency again? I played with the master branch before a bit and I could not see any circular require warnings.

[p-datadog]

The technical circular dependency was removed in 43e1f23#diff-6566ed78aec0d0209e0f3b7776e7db57d4694f438d12d3b6b9312f1209bfd994L3, specifically the require of 'datadog/core' from 'datadog/core/ddsketch'. However, 'datadog/core/ddsketch' still references Datadog::Core, but now without the require being present.

So, technically, the circular dependency is there, but not in 'require' form at the moment.

[ivoanjo]

Oh, right, I understand. Indeed Datadog::Core::DDSketch.supported? would break unless core was loaded.