Drop the dead std.fmt fallback in the emitter's integer writer

Five digits is every u16, so the `v >= 10000` branch could never be taken and it was
dragging `std.fmt.printInt` into a firmware whose whole reason for hand-rolling this
was to keep the format machinery out of the hottest sequence it emits.

Behaviour is identical, and re-verified rather than assumed: screen byte-identical to
the vaxis reference on the 18-step workload, round trip median 3830 us over 60 trials
(3829 before), snap 95/95, hxdiff 481/0, hxparity 561/0, unit-test.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/p4.zig b/src/p4.zig
index 0f23ddd5..5319ad90 100644
--- a/src/p4.zig
+++ b/src/p4.zig
@@ -722,8 +722,9 @@ fn cup(row: u16, col: u16) !void {
     try emitRaw(b[0..i]);
 }
 
+/// Decimal, least significant digit first into a scratch buffer and then reversed. Five digits is
+/// every `u16`, so there is no fallback to `std.fmt` and no value this cannot write.
 fn dec(buf: []u8, v: u16) usize {
-    if (v >= 10000) return std.fmt.printInt(buf, v, 10, .lower, .{});
     var digits: [5]u8 = undefined;
     var n: usize = 0;
     var rest = v;