fix otel sampling inheritance

[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 golangci-lint run 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: 2025-07-03 18:40:20

Comparing candidate commit 1205a4a in PR branch mtoff/fix-otel-sampling with baseline commit ef46958 in branch main.

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

[darccio]

@mtoffl01 Shall we close this PR in favour of #3856?

[darccio]

@genesor @mtoffl01 Should we keep this PR?

[darccio]

Closing this PR along with 3917.