chore(transport): Handle HTTP 413 response for oversized envelopes

[sl0thentr0py]

Description

Handle HTTP 413 (Content Too Large) responses from Relay. Previously, oversized envelopes returned HTTP 400 from Relay. Now that Relay returns 413, the SDK can distinguish size-related rejections from other errors.

Changes:

• When the transport receives an HTTP 413 response, log a warning: "HTTP 413: Envelope dropped due to exceeded size limit" (with response body if available)
• Record client reports with reason send_error for each dropped item (so Sentry can track data loss)
• Do NOT retry on 413 — the data is definitively too large
• The 413 check comes before the existing 429 rate-limit check in the response handling flow
• Added SizeExceededError exception class (subclass of ExternalError) for internal flow control
• Added :send_error to the CLIENT_REPORT_REASONS list

Closes #2844

References

• Python: feat(transport): Report 413 responses for oversized envelopes sentry-python#5380
• Go: feat: log specific message for RequestEntityTooLarge sentry-go#1185

Test plan

• Added tests for 413 response handling with body present
• Added tests for 413 response handling with empty body
• Added tests verifying client reports are recorded with send_error reason
• Added tests verifying send_envelope does not re-raise the error
• All existing transport tests continue to pass (65 examples, 0 failures)

🤖 Generated with Claude Code

[sl0thentr0py]

reviewed and approved from me since this is a claude PR