feat: Added 'FOR UPDATE SKIP LOCKED' to SelectQuery

[bbldn]

• Added 'FOR UPDATE SKIP LOCKED' and 'FOR UPDATE NOWAIT' to SelectQuery

🤔 Why?

Issues240

[roxblnfk]

I think it's time to increase min PHP version to 8.1 and use enums.

/**
 * Row-level lock strength.
 * PG-specific modes fallback to Update/Share on other drivers.
 */
enum LockMode
{
    /** Exclusive lock. Blocks UPDATE, DELETE, SELECT FOR UPDATE/SHARE. */
    case Update;

    /** Shared lock. Blocks UPDATE, DELETE, SELECT FOR UPDATE. Allows FOR SHARE. */
    case Share;

    /**
     * PG only. Like Update, but doesn't block FOR KEY SHARE.
     * Use when not modifying PK/FK columns.
     * Fallback: Update (MySQL, MSSQL), noop (SQLite).
     */
    case NoKeyUpdate;

    /**
     * PG only. Weakest lock — blocks only DELETE and PK/FK updates.
     * Fallback: Share (MySQL, MSSQL), noop (SQLite).
     */
    case KeyShare;
}

/**
 * Lock wait behavior when row is already locked.
 */
enum LockBehavior
{
    /** Default. Block until lock is released. */
    case Wait;

    /**
     * Fail immediately if row is locked.
     * PG: NOWAIT, MySQL: NOWAIT, MSSQL: SET LOCK_TIMEOUT 0.
     * SQLite: NotSupportedException.
     */
    case NoWait;

    /**
     * Skip locked rows, return only unlocked. Useful for job queues.
     * PG: SKIP LOCKED, MySQL: SKIP LOCKED (8.0+), MSSQL: READPAST hint.
     * SQLite: NotSupportedException.
     */
    case SkipLocked;
}

interface SelectQuery
{
    // ...

    /**
     * Add row-level locking clause.
     *
     * @param LockMode $mode Lock strength. SQLite: ignored, uses BEGIN IMMEDIATE.
     * @param LockBehavior $behavior Wait strategy. SQLite: only Wait supported.
     */
    public function forUpdate(
        LockMode $mode = LockMode::Update,
        LockBehavior $behavior = LockBehavior::Wait,
    ): self;
}

// Usage
$query->forUpdate(LockMode::Update, LockBehavior::SkipLocked);

Feel free to use enums in this PR, the PHP version must be bumped separately.

[bbldn]

Ready. Maybe we should add method lock($mode, $behavior) and deprecate forUpdate()? And rename field $forUpdate to $lock?