Never return pooled Uint8Array instances

[ChALkeR]

Node.js codepaths might be returning pooled buffers which we are then casting to Uint8Arrays, which is cursed.

When the user requests to typecast to a Buffer, returning pooled Buffers on Node.js is acceptable as that's what Buffer.from does

Not only TextEncoder, but likely none of the APIs should return pooled Uint8Arrays

Changes:

• f96a152, eaafab6 - fromHex
• 887d526 - fromBase58Check
• ... TODO

Tests only:

• 515007a - fromBase58
• a4a5bdf - fromWifString