feat: Add gateway endpoints

[Jiralite]

Please describe the changes this PR makes and why it should be merged:
https://discord.com/developers/docs/events/gateway has endpoints we could add!

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating
• This PR changes the library's interface (methods or parameters added)

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2 Skipped Deployments

Project	Deployment	Preview	Comments	Updated (UTC)
discord-js	Ignored	Preview		Oct 4, 2025 4:33pm
discord-js-guide	Ignored	Preview		Oct 4, 2025 4:33pm

[codecov]

Codecov Report

❌ Patch coverage is 5.88235% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.31%. Comparing base (d251e06) to head (b28e71d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/core/src/api/gateway.ts	5.88%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11130      +/-   ##
==========================================
- Coverage   44.34%   44.31%   -0.04%     
==========================================
  Files         312      313       +1     
  Lines       18016    18033      +17     
  Branches     1791     1791              
==========================================
+ Hits         7990     7991       +1     
- Misses      10014    10030      +16     
  Partials       12       12              

Flag	Coverage Δ
brokers	26.29% <ø> (ø)
core	0.92% <5.88%> (+0.03%)	⬆️

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