Decode base64 from an owned Vec (in-place whitespace strip + decode).
Avoids a full buffer copy by stripping whitespace in the existing allocation,
then decoding in-place. Ideal when the caller already has an owned Vec.
Stream-decode from a reader to a writer. Used for stdin processing.
Reads all input, strips whitespace, decodes in one SIMD pass, writes once.
The caller is expected to provide a suitably buffered or raw fd writer.
Decode base64 data and write to output (borrows data, allocates clean buffer).
When ignore_garbage is true, strip all non-base64 characters.
When false, only strip whitespace (standard behavior).
Stream-encode from a reader to a writer. Used for stdin processing.
Uses 4MB read chunks and batches wrapped output for minimum syscalls.
The caller is expected to provide a suitably buffered or raw fd writer.