deps: bump zspec v0.9.1 → v0.9.2 — fixes Linux CI deadlock

zspec v0.9.1's `.simple`-mode runner left `std.testing.io_instance`
uninitialized; any test reaching for `std.testing.io` (we have one:
`saveFlow + loadFromFile round trip via tmpDir`) tried to enqueue work
onto a zero-init `Io.Threaded` pool, which deadlocks on Linux but
silently succeeds on macOS. CI runs hung 50-60min until the 10-min cap.

zspec#44 fixed it in v0.9.2 by initializing `std.testing.io_instance`
at the top of `runner.zig:main()` and deinit'ing on return (mirroring
the stdlib terminal test runner). flow-codegen was on the pre-fix
v0.9.1; bumping picks up the fix.

Tests pass locally (89/89, 128ms). The 10-min CI cap stays in place
as a safety net.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: apotema

build.zig.zon

@@ -5,8 +5,8 @@
     .minimum_zig_version = "0.15.2",
     .dependencies = .{
         .zspec = .{
-            .url = "https://github.com/apotema/zspec/archive/v0.9.1.tar.gz",
-            .hash = "zspec-0.9.1-jaKLbbX4AwBKANdetxzzWc3UTO0UY0lcJJzTagQHlt5K",
+            .url = "https://github.com/apotema/zspec/archive/v0.9.2.tar.gz",
+            .hash = "zspec-0.9.1-jaKLbXgMBACFwbNjflhbMyP113leoYjboxn-1UOP-FGw",
         },
     },
     .paths = .{