chore: deprecate the span= arguments on ExecutionContext methods

[emmettbutler]

This pull request deprecates the span arguments on ExecutionContext methods to indicate that they are only for backward compatibility and not meant to be used by newly written code. This has been the plan since the beginning of the core API in #6202 (comment).

Deprecations are usually used for non-internal functionality, but I think a deprecation is appropriate in this internal case as we encourage broader usage of the core API.

This changed caused a failure in the fastapi framework test suite, which I think is the result of that test being too strict in its expectations. This pull request skips that test and adds a fallback that avoids the deprecation warning when fastapi is loaded. I've also opened tiangolo/fastapi#10876 making the fastapi framework test more permissive.

Checklist

• Change(s) are motivated and described in the PR description.
• Testing strategy is described if automated tests are not included in the PR.
• Risk is outlined (performance impact, potential for breakage, maintainability, etc).
• Change is maintainable (easy to change, telemetry, documentation).
• Library release note guidelines are followed. If no release note is required, add label changelog/no-changelog.
• Documentation is included (in-code, generated user docs, public corp docs).
• Backport labels are set (if applicable)

Reviewer Checklist

• Title is accurate.
• No unnecessary changes are introduced.
• Description motivates each change.
• Avoids breaking API changes unless absolutely necessary.
• Testing strategy adequately addresses listed risk(s).
• Change is maintainable (easy to change, telemetry, documentation).
• Release note makes sense to a user of the library.
• Reviewer has explicitly 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
• If this PR 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.
• This PR doesn't touch any of that.

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-01-02 20:08:38

Comparing candidate commit e29200b in PR branch emmett.butler/deprecate-core-span with baseline commit 14d3cbc in branch main.

Found 3 performance improvements and 8 performance regressions! Performance is the same for 184 metrics, 9 unstable metrics.

scenario:coreapiscenario-get_item_exists

• 🟥 execution_time [+98.426ns; +103.909ns] or [+18.385%; +19.409%]

scenario:coreapiscenario-get_item_missing

• 🟥 execution_time [+92.209ns; +102.764ns] or [+15.075%; +16.801%]

scenario:flasksimple-appsec-get

• 🟩 max_rss_usage [-992.084KB; -832.275KB] or [-2.751%; -2.308%]

scenario:flasksimple-appsec-post

• 🟩 max_rss_usage [-1.190MB; -0.972MB] or [-3.294%; -2.692%]

scenario:flasksimple-baseline

• 🟥 max_rss_usage [+730.612KB; +926.220KB] or [+2.063%; +2.615%]

scenario:otelspan-add-metrics

• 🟥 execution_time [+6.591ms; +11.302ms] or [+2.453%; +4.207%]

scenario:otelspan-add-tags

• 🟥 execution_time [+7.656ms; +11.599ms] or [+3.091%; +4.683%]

scenario:otelspan-start

• 🟥 execution_time [+7.970ms; +10.751ms] or [+17.714%; +23.893%]
• 🟩 max_rss_usage [-5.402MB; -5.213MB] or [-10.625%; -10.253%]

scenario:otelspan-start-finish

• 🟥 execution_time [+9.187ms; +10.718ms] or [+12.493%; +14.575%]

scenario:otelspan-start-finish-telemetry

• 🟥 execution_time [+9.347ms; +10.643ms] or [+12.744%; +14.512%]