Throttle our retries when attempting cross-signing reset, and give up after a time limit

[andybalaam]

Related to element-hq/element-x-android#6420

Part of element-hq/element-x-android#5075

I noticed when investigating a bug about resetting your identity when using a MAS login that we poll the server checking whether the user has given us permission with no limit on how fast we poll, and with no ability to give up if it's not working.

This change causes us to retry only twice per second, and give up after 2 minutes. These are guesses as to the right values and I am open to discussion.

• I've documented the public API Changes in the appropriate CHANGELOG.md files.
• This PR was not made with the help of AI.

[Hywan]

Approving but can't we use the backoff mechanism we have in the HTTP client instead?

[codspeed-hq]

Merging this PR will improve performance by 98.97%

⚡ 1 improved benchmark
✅ 49 untouched benchmarks

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	Restore session [memory store]	222.9 ms	112 ms	+98.97%

---

_{Comparing andybalaam/throttle-cross-signing-reset (89b7603) with main (cbfecf5)}

[andybalaam]

Approving but can't we use the backoff mechanism we have in the HTTP client instead?

Hmm, I'm not sure. We want to keep polling fast because at some point the user will click the button in MAS and we want to respond quickly when that happens.

[codecov]

Codecov Report

❌ Patch coverage is 70.83333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.80%. Comparing base (84ddafb) to head (89b7603).
⚠️ Report is 3 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
crates/matrix-sdk/src/encryption/mod.rs	70.83%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6325      +/-   ##
==========================================
- Coverage   89.82%   89.80%   -0.02%     
==========================================
  Files         376      376              
  Lines      102591   102601      +10     
  Branches   102591   102601      +10     
==========================================
- Hits        92152    92144       -8     
- Misses       6857     6872      +15     
- Partials     3582     3585       +3     

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[poljar]

Yup