refactor(profiler): alternative zstd encoder reuse approach

[felixge]

What does this PR do?

Refactor the zstd encoder sharing implemented in #4058 by assigning acquire/release semantics to the compressor interface Reset / Close methods.

Motivation

Hide the implementation details of the shared encoder from the profile type implementations. Also properly support multiple zstd levels for different profile types. This is not needed for now, but the current interfaces expect this ability to work. If we want to constrain this in the future, we should do it on the interface level first.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• New code is free of linting errors. You can check this by running ./scripts/lint.sh locally.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

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[pr-commenter]

Benchmarks

Benchmark execution time: 2025-10-28 09:34:28

Comparing candidate commit 1079a3d in PR branch felix.geisendoerfer/alternative-zstd-encoder-reuse-approach with baseline commit a6be279 in branch PROF-12641-shared-zstd-encoder.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 24 metrics, 0 unstable metrics.

[datadog-datadog-prod-us1]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

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[Copilot]

Pull Request Overview

This PR refactors the zstd encoder sharing mechanism by replacing a global mutex-based approach with a builder pattern that assigns acquire/release semantics to the compressor interface's Reset/Close methods.

Key Changes:

• Introduced compressionPipelineBuilder to manage shared zstd encoders per compression level
• Replaced global compressionMux with per-encoder semaphores embedded in sharedZstdEncoder
• Updated all compression usage sites to call Close() after Reset() to properly release encoder resources

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
profiler/compression.go	Implements new compressionPipelineBuilder and sharedZstdEncoder types with semaphore-based encoder sharing
profiler/profiler.go	Uses compressionPipelineBuilder instance to build compression pipelines
profiler/profile.go	Removes global mutex locking and adds deferred Close() calls for resource release
profiler/compression_test.go	Updates tests to use new builder pattern

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[Copilot]

Pull Request Overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

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[nsrip-dd]

Nice refactor. Thanks!