fix(profiling): serialisable stack key [backport 2.6]

[github-actions]

Backport c91c077 from #8618 to 2.6.

Backport of #8435 to 2.7

Ensure that the stack key used to group events is actually hashable.

Testing strategy

This is an attempt to mitigate #8218, for which we don't have a reproducer. Should the issue occur again, we should be able to act on any future reports with the extra context that this proposed change provides.

Checklist

• Change(s) are motivated and described in the PR description
• Testing strategy is described if automated tests are not included in the PR
• Risks are described (performance impact, potential for breakage, maintainability)
• Change is maintainable (easy to change, telemetry, documentation)
• Library release note guidelines are followed or label changelog/no-changelog is set
• Documentation is included (in-code, generated user docs, public corp docs)
• Backport labels are set (if applicable)
• If this PR changes the public interface, I've notified @DataDog/apm-tees.
• If change touches code that signs or publishes builds or packages, or handles credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.

Reviewer Checklist

• Title is accurate
• All changes are related to the pull request's stated goal
• Description motivates each change
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Change is maintainable (easy to change, telemetry, documentation)
• Release note makes sense to a user of the library
• 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

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: backport-8618-to-2.6
Commit report: 012ec5f
Test service: dd-trace-py

✅ 0 Failed, 1036 Passed, 20 Skipped, 1h 26m 32.39s Total duration (4m 2.01s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-03-06 14:55:41

Comparing candidate commit 012ec5f in PR branch backport-8618-to-2.6 with baseline commit adff8da in branch 2.6.

Found 8 performance improvements and 4 performance regressions! Performance is the same for 181 metrics, 9 unstable metrics.

scenario:coreapiscenario-context_with_data_listeners

• 🟩 max_rss_usage [-745.842KB; -668.097KB] or [-3.412%; -3.057%]

scenario:coreapiscenario-context_with_data_no_listeners

• 🟩 max_rss_usage [-757.404KB; -685.207KB] or [-3.464%; -3.134%]

scenario:coreapiscenario-core_dispatch_listeners_and_all_listeners

• 🟩 max_rss_usage [-727.683KB; -658.404KB] or [-3.330%; -3.013%]

scenario:coreapiscenario-core_dispatch_only_all_listeners

• 🟩 max_rss_usage [-722.394KB; -650.994KB] or [-3.304%; -2.977%]

scenario:httppropagationextract-datadog_tracecontext_tracestate_not_propagated_on_trace_id_no_match

• 🟥 max_rss_usage [+670.703KB; +752.657KB] or [+3.177%; +3.565%]

scenario:otelspan-start

• 🟩 max_rss_usage [-3.325MB; -3.247MB] or [-7.749%; -7.567%]

scenario:sethttpmeta-no-useragentvariant

• 🟩 max_rss_usage [-654.610KB; -579.924KB] or [-2.959%; -2.622%]

scenario:sethttpmeta-obfuscation-regular-case-implicit-query

• 🟩 max_rss_usage [-782.453KB; -715.454KB] or [-3.505%; -3.205%]

scenario:sethttpmeta-obfuscation-worst-case-explicit-query

• 🟩 max_rss_usage [-738.378KB; -657.129KB] or [-3.309%; -2.945%]

scenario:sethttpmeta-useragentvariant_exists_2

• 🟥 max_rss_usage [+729.215KB; +801.460KB] or [+3.412%; +3.750%]

scenario:sethttpmeta-useragentvariant_exists_3

• 🟥 max_rss_usage [+704.743KB; +781.286KB] or [+3.295%; +3.653%]

scenario:sethttpmeta-useragentvariant_not_exists_2

• 🟥 max_rss_usage [+675.569KB; +753.116KB] or [+3.155%; +3.517%]