Prevent sending corrupt data to em4x70 w/`--par` option

[henrygab]

This is the first PR related to #2376 .

• Prevents sending corrupt data with minimal code change.
• Fixes em4x70 firmware to return PM3_* value (not boolean). Thanks to @iceman1001 for noting these errors so they could be fixed!
• Adds help text for third key, which is specifically optimized for lf em 4x70 autorecover

NOTE: MacOS builds fail due to Python install issue. This is fixed with PR #2380. Even so, linked are GitHub action results from a branch with one extra commit that disables the broken HiTag2 test:

• ✅ Ubuntu Build and Test
• ✅ Windows Build and Test
• ❌ MacOS Build and Test

future work

If hardware is found that requires this option, a later PR may re-enable this option. Alternatively, a later PR may entirely remove the `--par` option from `lf em 4x70`.

[github-actions[bot]]

You are welcome to add an entry to the CHANGELOG.md as well

[iceman1001]

Excellent!