spec runner: per-test timing always reports 0.00 ms (Zig 0.16 migration)

[tsunaminoai]

In src/root.zig (~line 738), runSpecTest has:

// TODO(zig-0.16-migration): std.time.nanoTimestamp removed; thread io to use std.Io.Timestamp.now.
const t1: i128 = 0;

std.time.nanoTimestamp() was removed in Zig 0.16. The replacement is std.Io.Timestamp.now(io, .monotonic) from std.Io, which requires threading an io: std.Io context through the spec runner call chain.

Fix: Accept std.process.Init.Minimal in main.zig and thread io through to runSpecTest.

Impact: Cosmetic only — spec results and pass/fail counts are fully correct. The per-test timing column in zig build spec always shows 0.00 ms.