Fix Sentry privacy for oversized structured logs - #441

Sentry truncates rendered JSON before before_send, which could bypass structured-field redaction and skip_sentry for oversized logs. Parse the complete original LogRecord when available, retaining the event fallback and ordinary stdlib truncation.

Regression tests verify final serialized-envelope redaction and suppression across the configured string limit, with stacktraces on and off. They also check stdout, stored exception metadata, and callback order.

Closes #432.

Validation:

• Full suite: 636 passed, 100% coverage.
• Sentry tests: 52 passed on both 2.70.0 and 2.73.0.
• Tracked-file formatting, lint, and type checks passed. The pre-existing untracked research note prevents the workspace-wide formatting check from passing; it is excluded from this PR.
• Standards and spec reviews: no findings.