Sweep: four-branch (Str*/Zstr/char*/(Zstr,len)) dispatch for remaining string-input APIs

[brightprogrammer]

Every string-input API should expose the four effective branches of the
StrCmp shape:

1. Str * — owned string
2. Zstr — NUL-terminated const char *
3. char * — MSVC string-literal synonym for Zstr (kept deliberately; see Zstr.h)
4. (Zstr, len) — fixed-length view, as a separate OVERLOAD arity → a _cstr worker

Implementation rule for the (Zstr, len) worker

Make a transient copy only if required:

• byte compare / scan callee → thread the bound via ZstrCompareN (or a
  length-bounded loop) with an exact-length guard — no copy.
• Str-taking callee → the existing StrInitFromCstr(ptr, len, alloc)
  transient-copy idiom (mirror the _zstr sibling) — never a hand-built
  Str / __magic internals poke.
• NUL-terminating syscall (open/mkdir/…) → bounded stack-buffer copy
  (file_open_n template).

Private snake_case workers live in each module's Private.h.

Done (PR #44)

File (FileOpen, FileReadAndClose), Elf (ElfOpen), ProcMaps; and Dir,
Dns, KvConfig, MachO, Http, Pe, Pdb, Socket.

Remaining — the sweep this issue tracks

• Std/Container/Str/Ops — StrSplit, StrSplitToIters (no length form)
• Std/Container/Str/Insert — has _4 counted forms; audit for the full shape
• Std/Container/Int/Convert — IntFromStr / IntTryFromStr families
• Std/Container/Float/Convert
• Std/Container/BitVec/Convert — partial; complete + audit
• Std/Io
• Std/File — FileWriteAndClose (from_buf / from_str / from_bytes)
• Parsers/Elf — ElfFindSection

Audit path (run per module after adding)

Str-taking macro → four effective branches → correct expansion → transient copies only if required. This caught a real prefix false-match bug in
macho_find_section_cstr during the first batch, so audit the untested
_cstr forms line by line.