crypto: Rename PreviouslyVerified to VerificationViolation

[andybalaam]

Part of element-hq/element-meta#2526

For consistency with other places, we have now settled on VerificationViolation as the best way to express this situation.

• Public API changes documented in changelogs (optional)

[bnjbvr]

LGTM. Note that previously_verified returns quite a few matches with a plain grep, so consider whether you want to rename those also or not (and no need to ask for another review from me IMO, unless you're unsure/unclear about one thing in particular).

[codecov]

Codecov Report

Attention: Patch coverage is 84.61538% with 2 lines in your changes missing coverage. Please review.

Project coverage is 84.64%. Comparing base (c5f5bc8) to head (f1ea400).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...x-sdk-crypto/src/olm/group_sessions/sender_data.rs	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4067      +/-   ##
==========================================
- Coverage   84.66%   84.64%   -0.03%     
==========================================
  Files         269      269              
  Lines       28600    28600              
==========================================
- Hits        24215    24209       -6     
- Misses       4385     4391       +6     

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