Add extra checks for non-numeric values in weight and count fields during seedlot creation

[afpowell]

Description

Gives user an error message if they enter non-numeric values in the seed amount or weight fields, rather than allowing the seedlot to be created.

Closes #5149

Checklist

• Refactoring only
• Documentation only
• Fixture update only
• Bug fix
  • The relevant issue has been closed.
  • Further work is required.
• New feature
  • Relevant tests have been created and run.
  • Data was added to the fixture
    • Data was added via a patch in /t/data/fixture/patches/.
  • User-Facing Change
    • The user manual in /docs has been updated.
  • Any new Perl has been documented using perldoc.
  • Any new JavaScript has been documented using JSDoc.
  • Any new legacy JavaScript has been moved from /js to /js/source/legacy.

[alockrow]

Looks good. However, I noticed it won't accept a new seedlot with 0 count or 0 weight so there's now no option to make an empty seedlot. Is that a problem?

[afpowell]

That's a great point, and I should definitely check with the group about it at the ticket meeting. The empty seedlot creation using 0s being disallowed is the current behaviour on master and, in terms of this PR, we still probably don't want to allow this weird 'backdoor' way of creating them by inserting character strings that then get turned into NAs, but it's definitely worth a discussion as to whether this should be enabled (via legitimate means)