Add structured exception handling for lock operations

[antonkomarev]

Introduces a dedicated exception hierarchy for database lock operations, improving error handling clarity and providing better context for debugging lock-related failures.

Changes

New Exception Classes

• AbstractLockException — Base exception for all database lock-related errors

  • Thrown only for exceptional situations (database errors, connection issues)
  • NOT thrown for normal lock contention (methods return false instead)

• LockAcquireException — Thrown when lock acquisition fails due to database error

  • Includes static factory method fromDatabaseError() with lock key context
  • Wraps original exception for full error chain

• LockReleaseException — Thrown when lock release fails due to database error

  • Includes static factory method fromDatabaseError() with lock key context
  • Wraps original exception for full error chain

Updated Logic in PostgresAdvisoryLocker

• Lock acquisition/release methods now throw structured exceptions on database errors
• Exception messages include human-readable lock key for easier debugging
• Distinguishes between "lock unavailable" (returns false) vs "database error" (throws exception)

Test Coverage

• New test suite: PostgresAdvisoryLockerExceptionTest with 172 lines
• Validates exception throwing for acquire/release failures
• Tests exception context (messages, previous exception chain)

Documentation

• Updated CLAUDE.md with exception handling architecture notes