Don't unblock/resume within nested contexts

[hanjinliu]

Signals are unblocked on exit of blocked context, which will cause problematic signal emission within nested contexts.

from psygnal import Signal
class A:
    sig = Signal(int)
a = A()

a.sig.connect(print)

with a.sig.blocked():
    with a.sig.blocked():
        a.sig.emit(0)
    a.sig.emit(1)  # <----------- will be emitted

This PR fixes the problem above by checking if the signal is blocked first, and restore the original state on exit.

[tlambert03]

thanks @hanjinliu, good one.

looks like tests are failing, but it's not your fault. You've hit on a funny/unexpected bug in the compiled version that somehow didn't surface in #149

I can reproduce locally, and will try to fix and push soon

[tlambert03]

hey @hanjinliu ... I think I have a fix for the tests here, but can't merge to your PR. can you merge hanjinliu#1

[codecov]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage 👍

Coverage data is based on head (a6d3a76) compared to base (3f52065).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #150   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           14        14           
  Lines         1411      1418    +7     
=========================================
+ Hits          1411      1418    +7     

Impacted Files	Coverage Δ
src/psygnal/_signal.py	100.00% <100.00%> (ø)

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[tlambert03]

thanks @hanjinliu!