fix(voice): handle multiple transitions simultaneously

[Snazzah]

Please describe the changes this PR makes and why it should be merged:

This makes it so multiple transitions can be handled properly, according to the DAVESessionManager sample code. This changes the private property pendingTransition to pendingTransitions that hold a map of transitions. I don't think that constitutes a breaking change since its a private property.

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes

[vercel]

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Project	Deployment	Preview	Comments	Updated (UTC)
discord-js	Ready	Preview	Comment	Oct 23, 2025 4:21pm
discord-js-guide	Ready	Preview	Comment	Oct 23, 2025 4:21pm

[codecov]

Codecov Report

❌ Patch coverage is 0% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.51%. Comparing base (697556f) to head (49c7980).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/voice/src/networking/DAVESession.ts	0.00%	23 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11100      +/-   ##
==========================================
+ Coverage   44.19%   44.51%   +0.31%     
==========================================
  Files         313      312       -1     
  Lines       18092    17804     -288     
  Branches     1796     1786      -10     
==========================================
- Hits         7996     7925      -71     
+ Misses      10084     9867     -217     
  Partials       12       12              

Flag	Coverage Δ
voice	60.56% <0.00%> (+0.30%)	⬆️

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