feat(engine): anonymize-on-export

[sepehr-safari]

What

feat(engine): trace anonymization (S4 #42) — strip sensitive fields so a
trace can be shared safely.

Closes #42.

Changes

• src/ocpp/anonymize.zig — anonymizeToJson(value) / anonymizeJsonText(text)
  walk the parsed JSON and emit pretty (2-space) JSON, mirroring the toolkit's
  cli/commands/anonymize.ts:
  • Sensitive keys — idTag / identifier → "anonymized";
    chargePointSerialNumber / chargeBoxSerialNumber / stationId →
    "station-anon"; numeric transactionId → resequenced.
  • PII in strings — email → [redacted-email], phone → [redacted-phone],
    IPv4 → [redacted-ip]. Zig std has no regex, so each is a hand-rolled matcher
    run in three sequential left-to-right passes (JS global-replace semantics).
• Wired into ocpp.zig; CURRENT_STATE updated.

Mirroring the code, flagging the quirks

Two toolkit behaviors are reproduced deliberately and documented in-code, not
silently "fixed":

• Meter values are not transformed (the toolkit docstring claims they are).
• transactionId resequences per occurrence — repeated occurrences of the
  same id get different numbers, so correlation isn't preserved (matches
  txCounter.next++). A stable distinct-id mapping is a possible future
  enhancement.

Safety

• Bounded recursion depth (max_depth) for untrusted, deeply-nested input.
• Output is JSON-escaped and re-parses as valid JSON (round-trip tested).
• Pure / headless — no file I/O in the module (that's the CLI's job, feat(cli): headless CLI subcommands + parity table #45).

Tests

104/104 headless tests pass (native test -Dplatform=null); native check --strict clean; zig fmt clean. New coverage: sensitive-key replacement,
email/phone/IPv4 redaction, numeric meter-value preservation, per-occurrence
transactionId resequencing, JSON round-trip through nested arrays/objects with
escaping, and precise phone/IPv4 matcher boundaries.