fix: update letterparser, fixing a few bugs

[webbertakken]

Changes

• Upgrade mat-sz/letterparser from v0.10.0 to v1.5.0. Fixes are listed here

Test email confirmed to work.

Checklist

• [x] Read the contribution guide and accept the code of conduct
• [x] Readme (updated or not needed)
• [x] Tests (added, updated or not needed)

[pr-code-reviewer[bot]]

:wave: Hi there!

1. Ensure consistency in package versioning between package.json and yarn.lock for "letterparser" by updating both to "^0.1.5".
2. Confirm version consistency for "util" package across files.
3. Verify compatibility with the updated dependencies for potential functionality or compatibility issues.

_{^{Automatically generated with the help of gpt-3.5-turbo. Feedback? Please don't hesitate to drop me an email at webber@takken.io.}}