Is your feature request related to a problem? Please describe.
Yes. I would like a deterministic log output so that repeated runs of an application with the same input results in the same output.

As an example: when doing repeated runs of a backtest, where the logged timestamp is controlled by the timestamps in the recorded market data file, the log output is always exactly the same except for one thing, the thread_id.

Describe the solution you'd like
Rather than always using the current pid/tid, have an option to use an incrementing integer

QUILL_NODISCARD QUILL_EXPORT QUILL_ATTRIBUTE_USED inline uint32_t get_thread_id() noexcept
{
#if defined(QUILL_USE_SEQUENTIAL_THREAD_ID)
    static std::atomic<uint32_t> next_thread_id = 0;
    return ++next_thread_id;
#elif defined(__CYGWIN__)
    ... etc
#endif
}

Additional context
This means that repeated runs will always have eg: 1 for the main thread, and 2 for next next spawned thread, etc.