chore: clarify usage and wording for current_root_span

[wantsui]

Following up on #9758, our current definition of current_root_span is a bit misleading. This attempts to clarify the definition since in a distributed trace, you can't actually use this to grab the root span. (The only thing it consistently returns is "local root").

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/_trace/tracer.py                                                @DataDog/apm-sdk-api-python

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-08 21:44:44

Comparing candidate commit a8486ab in PR branch wantsui/clarify-current-root-span with baseline commit 6c61f40 in branch main.

Found 2 performance improvements and 1 performance regressions! Performance is the same for 391 metrics, 2 unstable metrics.

scenario:iast_aspects-ospathsplit_aspect

• 🟥 execution_time [+339.948ns; +412.243ns] or [+8.772%; +10.637%]

scenario:iast_aspects-ospathsplitext_aspect

• 🟩 execution_time [-445.651ns; -389.003ns] or [-11.098%; -9.687%]

scenario:iast_aspects-split_aspect

• 🟩 execution_time [-181.622ns; -149.493ns] or [-9.481%; -7.804%]

[wantsui]

/merge

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2025-01-08 15:43:32 UTC ℹ️ MergeQueue: waiting for PR to be ready

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2025-01-08 18:33:01 UTC ⚠️ MergeQueue: This merge request was unqueued

[email protected] unqueued this merge request

[wantsui]

/remove

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Devflow running: /remove

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2025-01-08 18:32:59 UTC ℹ️ Devflow: /remove

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: wantsui/clarify-current-root-span
Commit report: a8486ab
Test service: dd-trace-py

✅ 0 Failed, 87 Passed, 1468 Skipped, 3m 41.98s Total duration (35m 26.08s time saved)