Check for file changes (by sha256 hash) before vectorising

[Davidyz]

This PR stores the file hashes into the metadata.

On a supported collection, VectorCode will now compare the file hash and the hash stored in the database. If they're the same, they're considered to be the same file (unchanged), and the vectorisation will be skipped for this file.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.48%. Comparing base (cdeccee) to head (f443789).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #178      +/-   ##
==========================================
+ Coverage   99.28%   99.48%   +0.20%     
==========================================
  Files          22       22              
  Lines        1534     1548      +14     
==========================================
+ Hits         1523     1540      +17     
+ Misses         11        8       -3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.