Whitespace-tolerant decode

[dipu-bd]

Real-world Base64 (PEM, MIME, HTTP headers) carries \n and spaces, which the current decoders reject. Add an opt-in flag to skip whitespace during decode.

Architecture fit

• Opt-in ignoreWhitespace (a.k.a. relaxed) flag on the alphabet decoders, default false so shipped behavior is unchanged (contract invariant).
• Minimal scope: at least Base64/Base32/Base16; document which characters are treated as whitespace.

Effort: S–M

Checklist

• ignoreWhitespace flag on AlphabetDecoder (default false)
• Default (strict) output byte-identical to today — differential proof
• Tests: whitespace-laced PEM/MIME inputs decode correctly when opted in; still throw when not
• README / CHANGELOG / example updated
• Format / analyze / test (vm + node) green