`signature_adapter` causes significant overhead in hot transition paths

[ojomio]

Profiling shows that signature_adapter (dispatcher.py:203) accounts for
~30–50% of callback execution time in steady-state transitions.

The overhead comes from repeated use of inspect.signature and argument
binding on every callback invocation.

Each transition re-binds callback arguments dynamically, dominating CPU time
in high-frequency state machines.

Evidence

Flamegraph shows signature_adapter → inspect.signature → bind
as a wide frame in callback execution.

Suggested improvements

• Cache bound callback adapters at state-machine construction time
• Optionally allow users to disable signature binding entirely
• Document performance impact of flexible callback signatures

Impact

This significantly limits throughput for systems with frequent transitions
and makes the library unsuitable for performance-critical workflows.