fix(ci_visibility): handle rate limiting errors [backport #17170 to 4.5]

[gnufede]

Backport 0d92314 from #17170 to 4.5.

Description

HTTP 429 (Too Many Requests) responses from the Datadog backend were falling through to the >= 400 branch in the backend connector, classifying them as non-retriable CODE_4XX errors. This caused CI visibility data to be silently dropped whenever the backend applied rate limiting.

This fix:

• Adds RATE_LIMITED to ErrorType with a distinct internal value ("rate_limited")
• Handles 429 responses before the generic 4xx check and marks them as RATE_LIMITED
• Adds RATE_LIMITED to RETRIABLE_ERRORS so they are retried up to the existing retry limit
• Parses the X-RateLimit-Reset response header to use as the retry delay when present (supports both Unix timestamps and durations in seconds), falling back to exponential backoff otherwise
• Maps RATE_LIMITED to status_code_4xx_response in telemetry metrics for cross-language consistency

Testing

Unit tests added in tests/testing/internal/test_http.py covering:

• 429 retried then succeeds
• 429 hits retry limit
• X-RateLimit-Reset as Unix timestamp → correct computed delay
• X-RateLimit-Reset as duration in seconds → value used directly
• Retry delay capped at MAX_RETRY_AFTER_SECONDS
• Missing or invalid X-RateLimit-Reset → falls back to exponential backoff

Telemetry test updated in tests/testing/internal/test_telemetry.py to verify RATE_LIMITED maps to "status_code" in endpoint_payload.requests_errors and to "status_code_4xx_response" in per-request error metrics.

Risks

Low. The change only affects the retry path for a previously unhandled status code. All other status codes follow the same logic as before.

Additional Notes

• RATE_LIMITED intentionally uses the internal value "rate_limited" (distinct from CODE_4XX) to avoid Python enum aliasing, which would have made CODE_4XX an alias and caused all 4xx responses to be retried. The mapping to the canonical telemetry value is done explicitly at emission time in record_error().
• The retry delay parsed from X-RateLimit-Reset is capped at MAX_RETRY_AFTER_SECONDS (120s) to prevent unreasonable waits — e.g., an expired Unix timestamp being misinterpreted as a duration of billions of seconds.

[cit-pr-commenter-54b7da]

Codeowners resolved as

ddtrace/testing/internal/http.py                                        @DataDog/ci-app-libraries
ddtrace/testing/internal/telemetry.py                                   @DataDog/ci-app-libraries
releasenotes/notes/ci-visibility-handle-rate-limiting-d7df3d047661bbd9.yaml  @DataDog/apm-python
tests/testing/internal/test_http.py                                     @DataDog/ci-app-libraries
tests/testing/internal/test_telemetry.py                                @DataDog/ci-app-libraries