chore: Convert buffer usage to Uint8Array

[acolytec3]

Fixes #303

Problems:

1. The enr packages references globalThis.Buffer in the base64 conversion utilities and this causes segmentation faults in the Ultralight hive tests
2. Buffer was only used for bytes (instead of Uint8Array) because of the requirements of bcrypto which only accepted Buffer as input.
3. The bigint-buffer package causes CI failures in Ultralight with arbitrary napi-ok === false errors that are indecipherable

Solution:

• Remove all Buffer types and utilities and replace with equivalent Uint8Arrays
• Switch toHex/fromHex usage to hexToBytes/bytesToHex from ethereum-cryptography
• Switch all utf8 conversion to ethereum-cryptography utf8ToBytes/bytesToUtf8 utilities
• Remove all references to globalThis.buffer
• Update base64 utilities conversion to use scure/base (author same as @noble/hashes)
• Remove bigint-buffer and replace with internal bigIntToBytes/bytesToBigInt conversion utilities

[acolytec3]

@wemeetagain Hopefully this isn't too far beyond what you had in mind with regard to #303. Removing buffers provided an opportunity to fix 2 other pain points for Ultralight. If the bigint-buffer performance drop you'll see from going over to the the bigint -> hex -> butes route is a concern, I'd be happy to look for ways to improve the performance though I think @paulm has done a pretty thorough job of squeezing all the performance he can out of that conversion process.