rework std.Io.Writer.Allocating to support runtime-known alignment

Also, breaking API changes to:
* std.fs.Dir.readFileAlloc
* std.fs.Dir.readFileAllocOptions
9a0970a12bAndrew Kelley committed on 8/30/2025, 7:48:50 AMparent79f267f
24 files changedLine totals unavailable