feat(boto3): Add ServiceExtension class

[pabloDeputter]

Description

Adds service-extension support to Boto3Integration. This keeps the generic Boto3 call lifecycle independent of individual AWS services.

• Adds _ServiceExtension interface for service-specific behavior through _get_span_config(), _get_request_attributes(), and _get_response_attributes(). This allows for custom span operations/origin, request attributes, and response/error attributes. A future method can also inject trace context into service-specific payload, e.g. SQS message attributes.
• Extensions are lazily imported (not sure whether this actually a good thing). Service modules are only imported on first use and falls back to generic behavior when service is unknown or broken.
• Generic attributes and errors remain authoritative over service-specific ones.

Issues

Resolves #7477

[github-actions]

Codecov Results 📊

✅ 130540 passed | ⏭️ 7171 skipped | Total: 137711 | Pass Rate: 94.79% | Execution Time: 454m 5s

All tests are passing successfully.

✅ Patch coverage is 85.00%. Project has 2557 uncovered lines.
✅ Project coverage is 90.29%. Comparing base (cc152e2) to head (2de4cfe).

Files with missing lines (3)

File	Patch %	Lines
sentry_sdk/integrations/boto3/_services/registry.py	61.11%	⚠️ 7 Missing and 1 partials
sentry_sdk/integrations/boto3/_instrumentation.py	93.75%	⚠️ 1 Missing and 2 partials
sentry_sdk/integrations/boto3/_services/base.py	88.89%	⚠️ 1 Missing

Coverage diff

@@            Coverage Diff             @@
##        master       #PR       +/-##
==========================================
+ Coverage    90.22%    90.29%    +0.07%
==========================================
  Files          194       201        +7
  Lines        25997     26323      +326
  Branches      9662      9752       +90
==========================================
+ Hits         23454     23766      +312
- Misses        2543      2557       +14
- Partials      1451      1461       +10

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