Fee abstraction fix

[brozorec]

1. Removed alternative wrapper paths (auth_user_and_invoke and collect_fee_then_invoke) and standardized to a single recommended helper: collect_fee_and_invoke.

   Reasoning:
   While we previously offered “flexibility” in how to compose authorization + fee-collection + invocation, it didn't provide meaningful practical benefits: implementers still had to manually construct authorization trees, which is complex and error-prone. Further, if approval is not bound atomically to the root call as a sub-invocation, it can open the door to front-running or a replay-style misuse. Long story short, the unopinionated approach, I was aiming for, turns out to be a possible footgun.

2. Added explicit expiration ledger validation for the case we don't rely on token.approve()

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.07%. Comparing base (e23aafa) to head (985c21c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #546      +/-   ##
==========================================
- Coverage   96.11%   96.07%   -0.04%     
==========================================
  Files          54       54              
  Lines        5245     5201      -44     
==========================================
- Hits         5041     4997      -44     
  Misses        204      204              

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