feat: make Signal and SignalInstance Generic, support static type validation of signal connections

[tlambert03]

supports the ability to perform static type checking on signal connection signatures

class Thing:
    sig = Signal(int, str)

t = Thing()

@t.sig.connect
def cb1() -> None: ...  # OK
@t.sig.connect
def cb2(a0: int) -> None: ...  # OK
@t.sig.connect
def cb3(a0: int, a1: str) -> None: ...  # OK

@t.sig.connect
def cb5(a0: int, a1: str, a2: float) -> None: ...  # ERR: too many params
@t.sig.connect
def cb6(a0: str) -> None: ...  # ERR: wrong type for a0

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.83%. Comparing base (8bf2d82) to head (44c222b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #304   +/-   ##
=======================================
  Coverage   99.82%   99.83%           
=======================================
  Files          22       22           
  Lines        2351     2365   +14     
=======================================
+ Hits         2347     2361   +14     
  Misses          4        4           

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[codspeed-hq]

CodSpeed Performance Report

Merging #304 will degrade performances by 52.55%

_{Comparing tlambert03:generic-signal (44c222b) with main (8bf2d82)}

Summary

⚡ 1 improvements
❌ 1 regressions
✅ 65 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	test_create_signal	62.8 µs	27.4 µs	×2.3
❌	test_create_signal_instance	34.8 µs	73.3 µs	-52.55%