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

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2 Skipped Deployments

Project	Deployment	Preview	Comments	Updated (UTC)
discord-js	Ignored	Preview		Sep 11, 2025 5:56pm
discord-js-guide	Ignored	Preview		Sep 11, 2025 5:56pm

[codecov]

Codecov Report

❌ Patch coverage is 0% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.45%. Comparing base (90aac12) to head (6461b79).

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   44.41%   44.45%   +0.03%     
==========================================
  Files         312      312              
  Lines       17900    17887      -13     
  Branches     1791     1791              
==========================================
  Hits         7951     7951              
+ Misses       9937     9924      -13     
  Partials       12       12              

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

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