Removes Option wrapper on AccountsDbConfig::bank_hash_details_dir

[brooksprumo]

Problem

The AccountsDbConfig::bank_hash_details_dir field is Option-wrapped only because Rust in versions 1.90 and older does not have a way to create a PathBuf in const contexts, which is needed for the ACCOUNTS_DB_CONFIG_FOR_TESTING/BENCHMARKS constants.

Summary of Changes

We're now on Rust 1.91.1, so remove the Option wrapper.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.5%. Comparing base (bba10d8) to head (5cff551).

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #9997     +/-   ##
=========================================
- Coverage    82.5%    82.5%   -0.1%     
=========================================
  Files         844      844             
  Lines      316757   316753      -4     
=========================================
- Hits       261599   261583     -16     
- Misses      55158    55170     +12     

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