perf: replace base64.h with simdutf SIMD-accelerated codec

[GrzywN]

Summary

Closes #42

Replaces the René Nyffenegger base64.h codec with simdutf v8.2.0 — the same SIMD-accelerated base64 library used internally by Node.js, Bun, and Deno. The library is vendored as an amalgamated single-file (simdutf.h + simdutf.cpp), keeping the same zero-external-dependency setup as before.

Encode (base64FromArrayBuffer) calls simdutf::binary_to_base64 directly.

Decode (base64ToArrayBuffer) mirrors V8's Uint8Array.fromBase64 implementation via simdutf::base64_to_binary_safe with loose last-chunk handling and decode_up_to_bad_char=true.

Behaviour changes (TC39-compliant)

Input	Before	After
Mid-string padding (SQ==QU0=)	silently decoded → [73, 65, 77]	throws Invalid base64
\n without removeLinebreaks	silently ignored	throws Invalid base64
\n with removeLinebreaks=true	stripped, decoded	stripped, decoded ✓
URL-safe chars (-_)	accepted	accepted ✓
Missing = padding	accepted (loose)	accepted (loose) ✓

Files changed

File	Change
cpp/simdutf.h	new — amalgamated header (v8.2.0)
cpp/simdutf.cpp	new — amalgamated implementation
cpp/base64.h	deleted
cpp/react-native-quick-base64.cpp	replace codec calls
android/CMakeLists.txt	base64.h → simdutf.cpp in sources
example/src/tests/corrupt.ts	update for TC39 behaviour
example/src/tests/linebreaks.ts	use MIME-style line-wrapped test data

iOS podspec (cpp/**/*.{h,cpp}) picks up simdutf.h/.cpp automatically — no podspec changes needed.

Screenshots

Android emulator	iPhone 16e simulator

[GrzywN]

The SQ==QU0= behaviour change is backed by the TC39 Uint8Array.fromBase64 spec (Stage 4, shipping in V8 & SpiderMonkey). The FromBase64 algorithm (§ 10.3) rejects any characters after a = padding sequence — making mid-string padding a hard error, not an implementation choice. RFC 4648 § 3.5 establishes the same rule at the wire level.

simdutf::base64_to_binary_safe with loose + decode_up_to_bad_char=true mirrors exactly what V8's ArrayBufferFromBase64 does internally, so toByteArray & Uint8Array.fromBase64 now produce identical results for the same input.

[craftzdog]

Amazing. Thanks!