ThreadPool-FP v0.9.1

v0.9.1 makes the project easier to enter and safer to monitor without changing
the established queueing, task, lifecycle, or error contracts.

Highlights

• A shorter README now leads with what the library does, one default path, and
  a complete copy-paste example.
• The Starter example is a small queue-and-wait program without interactive
  pauses or outdated error guidance.
• A new examples index organizes all 15 samples by learning goal.
• Bounded pools expose QueueCount, QueueCapacity, and QueueLoadFactor
  directly, so monitoring does not require access to the mutable queue object.
• BackpressureConfig is available directly on the pool and is protected by
  the queue lock.
• Duplicate callback work-item logic now lives in one internal unit.
• Obsolete test code and a timing-dependent unit assertion were removed.

Safe bounded-queue monitoring

WriteLn('Queued: ', Pool.QueueCount, '/', Pool.QueueCapacity);
WriteLn('Load: ', Pool.QueueLoadFactor:0:2);

Config := Pool.BackpressureConfig;
Config.MaxAttempts := 3;
Config.HighLoadDelay := 200;
Pool.BackpressureConfig := Config;

The legacy Pool.WorkQueue property remains available so existing v0.x source
continues to compile. New code should not mutate it: direct enqueue, dequeue, or
clear operations bypass the pool's completion counter and can invalidate
WaitForAll.

Documentation journey

The project documentation now has clearer roles:

• README.md answers what the library does and gets a new user
  to a running program.
• examples/README.md selects the next sample by goal.
• CHEATSHEET.md keeps operational rules on one page.
• The Simple, Producer-Consumer, and Tasks API documents remain the canonical
  detailed contracts.
• Technical guides and archived development plans serve maintainers without
  interrupting the beginner path.

Maintenance

ThreadPool.Internal.WorkItems now owns the common untracked callback wrapper.
The existing TSimpleWorkItem and TProducerConsumerWorkItem names remain as
compatibility wrappers. Shared ThreadCount and LastError properties now
come directly from TThreadPoolBase, eliminating redundant overrides.

The inactive legacy threadpooltests.pas suite was removed. The wall-clock
parallel-scaling assertion was also removed from FPCUnit; performance remains
covered by the dedicated benchmark project.

Compatibility

This is a source-compatible patch release. Existing programs can continue to
use:

• all Queue, TryQueue, Submit, TrySubmit, and SubmitRange overloads;
• WaitForAll, Shutdown, task handles, batches, cancellation, and errors;
• both pool constructors and GlobalThreadPool;
• the v0.8 IThreadPool interface and GUID; and
• legacy WorkQueue and TBackpressureConfig access.

Verification

The release gate builds the Lazarus package, runs all 81 active tests, builds
the benchmark, and builds all 15 examples. CI covers Windows and Linux.