feat: add metadata, user caching, improve event dispatch

[joshuasing]

Summary
Add user metadata system, add user caching, improve event dispatch, improve audience provider.

Fixes #216

Changes

• Add user metadata system (fix Metadata System #216)
• Add user caching
• Improve event dispatch
• Improve audience provider

Checklist

• I acknowledge and agree to the terms of the Developer Certificate of Origin.
• All contributed code can be distributed under the terms of the MIT License.
• I have read the contributing guidelines and code of conduct.
• I have checked the "Allow edit from maintainers" option.
• I have added appropriate unit tests for my changes.

[codecov]

Codecov Report

Merging #290 (7e6e0f0) into main (d21f5df) will increase coverage by 1.95%.
The diff coverage is 92.35%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #290      +/-   ##
============================================
+ Coverage     70.85%   72.80%   +1.95%     
- Complexity      405      500      +95     
============================================
  Files            72       83      +11     
  Lines          1513     1688     +175     
  Branches         87      106      +19     
============================================
+ Hits           1072     1229     +157     
- Misses          407      425      +18     
  Partials         34       34              

Files	Coverage Δ
...in/java/dev/hypera/chameleon/meta/MetadataKey.java	100.00% <100.00%> (ø)
...ava/dev/hypera/chameleon/meta/MetadataKeyImpl.java	100.00% <100.00%> (ø)
...v/hypera/chameleon/platform/PlatformChameleon.java	0.00% <ø> (ø)
...n/platform/adventure/PlatformAudienceProvider.java	100.00% <100.00%> (ø)
...platform/adventure/StandaloneAudienceProvider.java	100.00% <100.00%> (ø)
...meleon/platform/event/PlatformEventDispatcher.java	100.00% <100.00%> (ø)
...pera/chameleon/platform/user/PlatformChatUser.java	100.00% <100.00%> (ø)
...v/hypera/chameleon/platform/user/PlatformUser.java	100.00% <100.00%> (ø)
...a/chameleon/platform/user/PlatformUserManager.java	100.00% <100.00%> (ø)
...era/chameleon/platform/util/PlatformEventUtil.java	0.00% <ø> (ø)
... and 4 more

[LooFifteen]

Looks like a load of listeners don't ever get unregistered, which could cause problems when people are using plugins like Plugman. We should be handling support for these kind of plugins because the end user of Chameleon does not have the option to.