feat(rest): callbacks for timeout and retry backoff

[ckohen]

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

Adds two related utility options for managing rest requests more dynamically.
Retry Backoff is completely new, allows backing off on 5xx and aborted requests. Closes: #10571
timeout gets a callback utility, allows setting the timeout per request Closes: #10927 and supersedes #11013

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)

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

2 Skipped Deployments

Project	Deployment	Preview	Comments	Updated (UTC)
discord-js	Ignored	Preview		Sep 10, 2025 9:17am
discord-js-guide	Ignored	Preview		Sep 10, 2025 9:17am

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.12%. Comparing base (5d5a694) to head (3399c9d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/rest/src/lib/handlers/Shared.ts	62.50%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11067      +/-   ##
==========================================
- Coverage   44.27%   44.12%   -0.15%     
==========================================
  Files         312      310       -2     
  Lines       17851    17791      -60     
  Branches     1775     1766       -9     
==========================================
- Hits         7903     7851      -52     
+ Misses       9936     9928       -8     
  Partials       12       12              

Flag	Coverage Δ
core	0.88% <ø> (ø)
proxy	65.88% <ø> (ø)
rest	87.56% <77.77%> (+0.37%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Jiralite]

Does this address #11000?

[ckohen]

No, not at all. That requires a change in discord.js not rest (which I'll get to later today)

[didinele]

you mentioned changing a thing in kyra's thread, other than that, LGTM

Resolved