[garydgregory]

Add optional FIFO fairness to TimedSemaphore (LANG-1790).

Offered as an alternative to PR #1544

This changeset addresses LANG-1790 while preserving the existing default behavior and public API.

The main difference is that fairness is enforced by an explicit FIFO queue. In the original PR, callers still block on Object.wait(), while the backing Semaphore is only polled with immediate acquisition attempts. Those callers never join the semaphore’s waiting queue, so its fairness setting cannot enforce their acquisition order.

This implementation also:

• Keeps permit acquisition, accounting, limit changes, and period rollover under the same monitor, avoiding the race between consuming a permit and updating acquireCount.
• Preserves the non-throwing tryAcquire() signature and documents that it can bypass queued callers.
• Handles interruption and shutdown by removing the correct queue entry and notifying remaining callers.
• Preserves unlimited-mode behavior: new acquisitions proceed immediately, and existing waiters can proceed at rollover.
• Documents the actual ordering guarantee without referring to a timed tryAcquire() overload that this class does not provide.

The regression tests establish that callers are waiting before checking ordering. They cover newcomer bypass prevention, explicit non-fair behavior, cancellation, shutdown, limit changes, and builder reuse. A controlled test also distinguishes FIFO behavior from non-fair behavior without relying on thread-start order or unrestricted completion order.

The original enhancement request is valid; these changes make the fairness guarantee effective while avoiding compatibility and concurrency regressions.