fix two 0.16 build errors: trimLeft rename, @cImport failure
- broadcaster.zig: std.mem.trimLeft → std.mem.trimStart (0.16 rename)
- main.zig: replace @cImport(@cInclude("malloc.h")) with @extern
declaration for malloc_trim — zig 0.16 C translator fails on
glibc's stdio2.h (__builtin_va_arg_pack)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>