Stdlib: base64_encode() and base64_decode() VM + LLVM JIT/AOT #978

Problem

Web apps use base64 for tokens, Basic auth headers, and binary-safe transport. These functions are not in ext/standard/Module.php.

Goal

Native VM + LLVM JIT/AOT (no PHP internal_* wrappers), subset matching PHP 8:

• base64_encode(string $data): string
• base64_decode(string $data): string|false (non-strict; ignore chars outside alphabet)

Acceptance

• compliance + JIT PHPT, AOT fixtures, unit smoke
• ./script/ci-local.sh --filter base64 green in Docker

Related

• ROADMAP 🗺️ ROADMAP: Self-host + web-capable PHP subset (living) #78 Phase 2 Stdlib (encoding parity with bin2hex/hex2bin)