[utils] RegEx is slow (can we make faster hex functions?)

Nobody has claimed this yet.

Noticed a recent attempt at speeding up some functions by switching to RegEx. But RegExes are usually slower than iterating over strings.

For example, this function:

https://github.com/MetaMask/utils/blob/1bea7f378c37117260912af1921556bc57110d20/src/hex.ts#L60

Is probably about 4-5x slower than something like this:

```
function isHexAddress(str) {
if (typeof str !== "string" || str.length !== 42) return false;
if (str[0] !== '0' || str[1] !== 'x') return false;
for (let i = 2; i < 42; i++) {
let code = str.charCodeAt(i);
// numbers and lowercase a - f
if (!((code >= 48 && code <= 57) || (code >= 97 && code <= 102))) {
return false;
}
}
return true;
}
```

(don't take my word for it. this should be tested further)

Start at src/hex.ts around the linked function and identify the regex-based hex helpers involved. Benchmark the current behavior against the proposed string iteration, then verify that valid and invalid inputs retain their existing results. Done means the chosen change has measured performance evidence and preserves the helpers’ behavior.

Written by the indexing model from the issue text.