feat: adding trickle ice support

[rprata]

This commit enables Trickle ICE by allowing candidates to be exchanged incrementally between peers over the signaling channel.

[jlaine]

Hi! Could you please drop all the changes not related to actual ICE trickle and rebase on top of main?

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 99.83%. Comparing base (6ea9d7a) to head (b36da71).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/aioice/ice.py	83.33%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              main      #83      +/-   ##
===========================================
- Coverage   100.00%   99.83%   -0.17%     
===========================================
  Files            7        7              
  Lines         1232     1240       +8     
===========================================
+ Hits          1232     1238       +6     
- Misses           0        2       +2     

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[jlaine]

Hi @rprata ! I'm not sure I understand how this PR helps us: it does indeed "emit" candidates as it discovers them, but we're no closer to connecting while still gathering candidates. Unless I'm mistaken this is a much deeper change, because it means:

• Changing the internal state machine to allow building new candidate pairs while connecting.
• Changing the internal state machine to not fail if we reach the end of the check list while still gathering.
• Reworking the public API.