Add support for MySQL 8.0.1+ locking features (FOR SHARE, NOWAIT, SKIP LOCKED)

[StefanStuehrmann]

Overview

This PR enhances DBIx::Class's MySQL support by implementing the locking features introduced in MySQL 8.0.1:

• Adds support for the standard SQL-compliant FOR SHARE syntax (while maintaining backward compatibility with LOCK IN SHARE MODE)
• Implements NOWAIT modifier to fail immediately when encountering locked rows
• Implements SKIP LOCKED modifier to skip locked rows in the result set
• Adds support for the OF table_name clause to lock specific tables

[https://dev.mysql.com/blog-archive/mysql-8-0-1-using-skip-locked-and-nowait-to-handle-hot-rows/]

Implementation Details

The implementation introduces a flexible hash-based configuration for advanced locking options while maintaining backward compatibility with the existing string-based syntax:

# Basic usage (existing functionality)
$rs->find({...}, {for => 'update'});

# New standard shared lock (MySQL 8.0.1+)
$rs->find({...}, {for => 'share'});

# Advanced locking with modifiers
$rs->find({...}, {
  for => {
    type => 'update',
    modifier => 'nowait'
  }
});

# Locking specific tables
$rs->find({...}, {
  for => {
    type => 'share',
    of => ['table1', 'table2'],
    modifier => 'skip_locked'
  }
});

A deprecation warning has been added for the legacy shared option to encourage migration to the new standard share option.

Testing

Comprehensive test coverage has been added for all locking features, including:

• Basic locking options
• Hash-based configuration
• Modifiers (NOWAIT, SKIP LOCKED)
• Table specification with the OF clause
• Combinations of modifiers and table specifications

Motivation

These locking features are essential for building robust concurrent applications with MySQL 8.0.1+. The NOWAIT and SKIP LOCKED options are particularly valuable for implementing job queues and other high-concurrency patterns like exact once processing and helps avoiding deadlocks or long waits.

[StefanStuehrmann]

@ribasushi any chance you can review this change please? There are a lot of threaded / worker based applications out there relying on mysql so this feature allows to improve them without major redesign to become active/active.