Fix missing exception raise in `_val_is_numeric()` and `_val_is_str()`

[jrycw]

Hello Team,

While reviewing these two functions, I noticed that a ValueError exception is created but not raised.
I suspect this might be a bug, but please feel free to correct me if this behavior is intentional.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.91%. Comparing base (336e688) to head (837ca8f).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #510 +/- ## ======================================= Coverage 88.91% 88.91% ======================================= Files 44 44 Lines 5212 5212 ======================================= Hits 4634 4634 Misses 578 578 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.