[rennf93]

Closes #57

I audited guard-agent-rs against the Python agent (guard-agent master) and fixed every divergence I could reproduce. Each change has a test that failed on master first.

Redaction: Redactor now follows sanitize_headers. It recurses to depth 10 and redacts anything deeper wholesale, parses JSON-looking string values, sanitizes inside them and re-dumps them with Python's json.dumps formatting, redacts JSON-looking strings over 8192 characters wholesale, and applies the same rules to metric tag values. Strings that Python parses but serde_json cannot (lone surrogate escapes, nesting past the parser limit) are redacted wholesale instead of passing through, and the NaN and Infinity literals are handled. The transport runs a second pass over event metadata and metric tags before serializing, plain and encrypted. The expected values in tests/fixtures/sanitize_vectors.json come from running the reference function on the same inputs. serde_json gets preserve_order so re-dumped strings keep key order like Python.

Transport and flush:

• An encrypted batch answered with 413 is split and each half is re-encrypted, instead of being dropped with its Redis records.
• After a 413 split both halves are always sent, and the batch is confirmed only when both were.
• A dropped permanent rejection counts as sent, resets the flush streak and clears the retry gate.
• A rejected status push is a failed push.
• POST success is exactly 200 or 201. An unparseable 200, a 200 with an empty object, 202, 204, 3xx and other unlisted statuses are retried at once without backoff and without a breaker failure. A 200 body that is not an object is accepted, and errors uses Python truthiness. Redirects are no longer followed. GET follows the same status rules.
• The rules loop starts only when a project id is set.
• loop_failures.flush resets on every completed loop iteration, as in the reference, instead of counting failed flushes.
• An encryption key with surrounding whitespace is accepted.
• Docs: the signing note now says the Python agent also signs the uncompressed body, and AGENTS.md and CLAUDE.md no longer say version 0.1.0.

Existing tests that pinned the old behavior (drop does not count as sent, right half skipped, any 2xx accepted, rules loop without a project id) are updated to the reference behavior. I did not touch CHANGELOG.md because release prep owns it in this repo.

I ran fmt, clippy with -D warnings (default and all features), cargo test and cargo test --all-features -- --include-ignored against Redis, cargo doc with -D warnings, the MSRV 1.92 check and tests, cargo deny, cargo audit and the 100% line coverage gate locally.