chore: relative file paths in error messages

[anton-trunov]

Closes #406

• I have updated CHANGELOG.md
• [ ] I have added tests to demonstrate the contribution is correctly implemented: this usually includes both positive and negative tests, showing the happy path(s) and featuring intentionally broken cases I didn't add tests, just checked it works locally and it should be observable in CI in this check's error message. To properly test everything we should fix issue Add cram-like tests for Tact CLI #315
• I have run all the tests locally and no test failure was reported
• I have run the linter, formatter and spellchecker
• I did not do unrelated and/or undiscussed refactorings -- had to rename some errors because of introducing a parse error category