feat: PostgreSQL, try non-blocking query first to avoid race conditions

[seuros]

fixes #76 - Race condition in advisory_lock_exists?

[Copilot]

Pull Request Overview

This PR adds a non-blocking advisory lock existence check for PostgreSQL to avoid race conditions and updates the fallback to the original implementation. It also introduces multi-threaded tests covering both the new and fallback paths, plus minor cleanups in MySQL and the gemspec.

• Add advisory_lock_exists_for? in the PostgreSQL adapter for direct pg_locks queries
• Integrate the new method in advisory_lock_exists?, falling back when needed
• Introduce multi-threaded tests and a fallback exception test for PostgreSQL
• Remove unused helper in MySQL adapter and tweak gemspec formatting

Reviewed Changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
with_advisory_lock.gemspec	Adjusted heredoc formatting to preserve trailing spaces
test/with_advisory_lock/postgresql_race_condition_test.rb	Added tests for race conditions, detection, and fallback behavior
lib/with_advisory_lock/postgresql_advisory.rb	Implemented advisory_lock_exists_for? and simplified error guard
lib/with_advisory_lock/mysql_advisory.rb	Removed unused unique_column_name method
lib/with_advisory_lock/core_advisory.rb	Updated advisory_lock_exists? to prefer non-blocking check

Comments suppressed due to low confidence (1)

test/with_advisory_lock/postgresql_race_condition_test.rb:113

• The fallback test does not simulate a pg_locks access failure, so it never exercises the rescue path. Consider stubbing conn.advisory_lock_exists_for? to raise ActiveRecord::StatementInvalid and asserting that advisory_lock_exists? still returns a Boolean.

      assert_nothing_raised do