chore(config/tracer): migrate statsComputationEnabled

[mtoffl01]

What does this PR do?

Motivation

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: 2025-12-08 16:26:26

Comparing candidate commit 78baec5 in PR branch mtoff/statsComputationEnabled with baseline commit 85ac979 in branch mtoff/config-origin.

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

scenario:BenchmarkTracerAddSpans-25

• 🟥 execution_time [+87.546ns; +118.654ns] or [+2.513%; +3.405%]