perf: improve vanity address matching

[mattsse]

Motivation

the previous impl was a regex match on the address in hex format, which required additional allocs

Solution

this will try to match against the address bytes directly if the (start, end) are valid hex,
this means however, that odd patterns are still parsed via regex. this is probably faster for longer patterns than left|right padding

it accepts all combinations of --starts-with (hex|regex) --ends-with (hex|regex)

Example

cast wallet vanity --starts-with "0000"                                                                                                                                                         
Starting to generate vanity address...
Successfully found vanity address in 10 seconds.
Address: 0x00009AaB527c82E0ac9B53EB83DbBdd87aDeff14
Private Key: 0x637cbf8de182f697447b06bb2de563584b04b346500d140dbd25dc2d223366c1

[gakonst]

was this a meaningful perf improvement?

[mattsse]

hard to say, since the iterator always uses a new random key, but matching by comparing bytes of the address directly instead of comparing the allocated string via regex is definitely faster