refactor(Adapter): sendPayload now returns boolean

[amishshah]

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

Makes adapters easier to work with. At the moment, the only way to signal that a message cannot be sent via sendPayload is to destroy the whole adapter. This PR allows for sendPayload to return false if the message can definitely not be sent, and in this case, the voice connection enters the disconnected state rather than being destroyed entirely.

This means the developer has to call voiceConnection.reconnect() once the adapter later becomes available.

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• This PR changes the library's interface (methods or parameters added)
• This PR includes breaking changes (methods removed or renamed, parameters moved or removed)

[codecov]

Codecov Report

Merging #105 (316d825) into main (62cc43b) will decrease coverage by 0.26%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #105      +/-   ##
==========================================
- Coverage   63.69%   63.42%   -0.27%     
==========================================
  Files          18       18              
  Lines         807      812       +5     
  Branches      181      191      +10     
==========================================
+ Hits          514      515       +1     
- Misses        291      295       +4     
  Partials        2        2              

Impacted Files	Coverage Δ
src/VoiceConnection.ts	80.00% <100.00%> (+0.86%)	⬆️
src/audio/AudioResource.ts	95.34% <100.00%> (ø)
src/util/Secretbox.ts	35.29% <0.00%> (-23.53%)	⬇️

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