fix: updating cache after Import Signatures from File command

[ericleponner]

Description:

Changes below make sure that BackendTransactionCache is updated after import signatures from a files.
This enables correct state to be displayed in transaction details.

Related issue(s):

Fixes #2845

Notes for reviewer:

M   front-end/src/renderer/pages/Transactions/Transactions.vue
    # importSignaturesFromV2File() now makes sure to clear all cached data for the import transactions.

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.98%. Comparing base (6095dfa) to head (c618ed3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2846   +/-   ##
=======================================
  Coverage   99.98%   99.98%           
=======================================
  Files         184      184           
  Lines        7619     7619           
  Branches     1523     1538   +15     
=======================================
  Hits         7618     7618           
  Misses          1        1           

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[svienot]

LGTM