feat(rust-provider): add HTTP retry for flagLog writes

[nicklasl]

Summary

• Add retry with exponential backoff to LogSender::send() in the Rust provider, matching the JS provider's flagLog retry behavior
• 3 attempts, 500ms base delay, 2x backoff, ±10% jitter
• Retries on 5xx, 408, 429, and network errors; no retry on other 4xx
• Respects Retry-After header from server (takes precedence over computed backoff)
• Warns (not errors) after retries exhausted since log failures shouldn't disrupt flag evaluation

Test plan

• Unit tests for retry on 503, 429, 408
• Unit tests for no-retry on 400, 403
• Unit test for Retry-After header respect
• Unit tests for jitter bounds and parse_retry_after
• is_retryable_status coverage for all relevant codes
• Full crate test suite passes (95 tests)
• clippy clean

🤖 Generated with Claude Code

[nicklasl]

PR Updated ✅

Rebased onto current main (a866c61) and ported the retry logic to work with the new architecture.

Changes from original PR

The original PR was based on an older version of logger.rs. Since then, main added:

• Multi-destination support (Edge + Cloudflare)
• Fallback logic between destinations
• Per-destination encoding (protobuf vs ingest format)

What was done

✅ Ported retry-with-backoff logic onto the current architecture
✅ Retry now applies to both Edge and Cloudflare destinations
✅ Preserves fallback semantics (after retries exhausted on primary, fallback is still attempted)
✅ All tests passing (13 logger tests including 9 new retry tests)
✅ Clippy clean
✅ Now MERGEABLE (was CONFLICTING)

Test Results

test logger::tests::test_apply_jitter_within_bounds ... ok
test logger::tests::test_encode_ingest_request_empty_account_id ... ok
test logger::tests::test_encode_ingest_request_empty_batch ... ok
test logger::tests::test_encode_ingest_request_roundtrip ... ok
test logger::tests::test_is_retryable_status ... ok
test logger::tests::test_parse_retry_after ... ok
test logger::tests::no_retry_on_403 ... ok
test logger::tests::no_retry_on_client_error ... ok
test logger::tests::retries_on_429_and_succeeds ... ok
test logger::tests::retries_on_503_up_to_max_attempts ... ok
test logger::tests::retries_on_network_error ... ok
test logger::tests::respects_retry_after_header ... ok
test logger::tests::send_succeeds_on_first_attempt ... ok

test result: ok. 13 passed; 0 failed

Ready for review! 🚀

[nicklasl]

Fixed 🔧

Sorry about that! My first push accidentally uploaded file references instead of actual file contents (used @filename incorrectly with the API).

New commit: 4b5342d

Files are now correct:

• ✅ logger.rs: 17,919 bytes (was broken at 40 bytes)
• ✅ Cargo.toml: correct content
• ✅ README.md: correct content
• ✅ Cargo.lock: correct content

CI should pass now! 🤞