feat(common/lib/utils): catch error on bad b64 string inputs; add tests

[crookse]

Summary

Hi, I was working with Arweave transactions and my transactions were failing because I was passing in undefined tag values. Didn't catch this easily because my env was non-TS. The error message thrown wasn't too helpful (reading properties of undefined. reading 'replace'), so I'm proposing this error with a cause to improve and quicken the debugging process.

Did the following:

• Add UtilsError and throw it if decoding/encoding non-strings
• Add tests

[rosmcmahon]

firstly, sorry for the delay in reviewing this!
secondly, what function specifically were you calling that led on to this? yes, b64UrlEncode/b64UrlDecode can be called directly, but these are generally internal functions, so we might just be bubbling up a new equally confusing error message to the dev.
see this commit here for reference: 55a212a

[xgocn]

maybe the same situation? #228