Add caching to user experiments fetch function

[Dagonite]

Closes None (continuation of caching logic).

Description

Adds caching to the get_experiments_for_user_number function in the fia_api.core.auth.experiments module to improve efficiency by avoiding unnecessary API calls. Makes use of cache_get_json and cache_set_json, with a configurable TTL via the AUTH_EXPERIMENTS_CACHE_TTL_SECONDS environment variable. The function now first checks the cache before making an external request and caches successful responses.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.29%. Comparing base (d15484e) to head (a804704).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #595      +/-   ##
==========================================
+ Coverage   96.28%   96.29%   +0.01%     
==========================================
  Files          48       48              
  Lines        1882     1889       +7     
==========================================
+ Hits         1812     1819       +7     
  Misses         70       70              

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[Dagonite]

@copilot Why is the codecov failing?

[Copilot]

@Dagonite I've opened a new pull request, #597, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

Pull request overview

This PR adds caching functionality to the get_experiments_for_user_number function to reduce unnecessary API calls and improve performance. The implementation uses Redis/Valkey caching with a configurable TTL (default 120 seconds).

Changes:

• Added cache lookup before making external API requests using cache_get_json
• Implemented cache storage for successful API responses using cache_set_json
• Added configurable TTL via AUTH_EXPERIMENTS_CACHE_TTL_SECONDS environment variable
• Updated tests to cover caching scenarios including cache hits, misses, and failed requests

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
fia_api/core/auth/experiments.py	Adds caching logic with cache key generation, cache lookup, and cache storage for successful responses
test/core/auth/test_experiments.py	Adds comprehensive test coverage for caching behavior including cache hits, misses, and verification that failed requests are not cached

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