models/token: Remove unnecessary transaction

[Turbo87]

The transaction behavior was initially introduced in 52862fa and the commit message mentions:

Because our tests run in a single transaction, we need to wrap that update to ensure that the error doesn't poison the transaction.

but that first part is no longer true, so we don't need the transaction anymore AFAICT.

This PR also improves our test suite for this functionality a little to catch potential regressions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.11%. Comparing base (7ecdc11) to head (2e60082).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9559   +/-   ##
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  Coverage   89.11%   89.11%           
=======================================
  Files         285      285           
  Lines       28922    28942   +20     
=======================================
+ Hits        25774    25793   +19     
- Misses       3148     3149    +1     

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[Turbo87]

nevermind... I now understand the purpose of this transaction: if find_by_api_token() is used within an outer transaction then a failing update() would cause the outer transaction to be poisoned on the database side, even though the error is handled in the or_else() invocation on the app side.

TIL: transactions with only a single statement are not always as pointless as I thought...

I'll try to come up with a couple of tests for this behavior in a follow-up PR