Add AWS CloudTrail parser (JSON audit log)

[copyleftdev]

Implements the AWS CloudTrail plugin — issue #11.

What

A CloudTrail file is a single JSON document with a top-level Records array;
each record becomes one row, flattened depth-1:

• top-level scalars → columns (eventName, eventSource, sourceIPAddress, …);
• nested objects → parent.child columns (userIdentity.userName,
  userIdentity.type);
• anything deeper or array-valued (requestParameters, responseElements) →
  canonical JSON string, so a varied per-API payload doesn't explode the schema.

It also synthesizes eventEpoch — the RFC 3339 eventTime parsed to Unix
seconds via chrono (deterministic; no wall clock) — so --cadence eventEpoch
and the contextual detector (--period 24) can read the call series for
off-hours / automated-pattern anomalies, while eventName feeds rare-API dist
drift.

Routing

• Detected by a Records array whose entries carry eventName (STRONG),
  registered ahead of NDJSON/JSON.
• Claims no extension — CloudTrail is delivered as *.json (owned by the
  JSON parser); pipe it on stdin for CloudTrail-aware flattening.

Errors

Missing Records, a non-object record, and non-JSON are clean AxError::Parse.

Gates

• fmt / clippy -D warnings / full workspace tests green (both feature sets).
• Mutation gate: 0 surviving mutants on cloudtrail.rs. The extensions()
  → empty-slice mutant is a documented equivalent (same as Zeek/Journal/Eve).
• Smoke: a Records document routes as cloudtrail; an automated call burst is
  flagged by --cadence eventEpoch (exit 1).

Closes #11

🤖 Generated with Claude Code

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 672f74b3-4a5b-488a-84d1-31b17e7c1e8c

📥 Commits

Reviewing files that changed from the base of the PR and between 56747bb and 4fdc2d0.

📒 Files selected for processing (4)

• .cargo/mutants.toml
• crates/ax-normalize/src/parser.rs
• crates/ax-normalize/src/parsers/cloudtrail.rs
• crates/ax-normalize/src/parsers/mod.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/cloudtrail

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