terminal: dispatch APC string bytes in bulk slices

APC payloads such as Kitty graphics images can be megabytes of base64
data, but every byte was dispatched individually: through the VT state
machine table, an apc_put action, the stream handler, the APC protocol
handler, and finally a per-byte ArrayList append in the Kitty command
parser. Five layers of dispatch per byte made large image transfers
far slower than they needed to be.

Add a bulk fast path alongside the existing CSI fast paths in
consumeUntilGround: scan the longest run of apc_put bytes (stopping
at any byte the parse table doesn't treat as APC payload: CAN, SUB,
ESC, and most C1 bytes exit or abort the string state, and 0xA0-0xFF
are ignored by it) and dispatch the run as a single new apc_put_slice
action. The APC handler identifies the protocol from the first few
bytes as before, then passes the remainder of each slice to the
protocol parser in bulk; the Kitty parser appends payload data with a
single appendSlice. Ignored/unknown APC sequences now drop each slice
in O(1) instead of per-byte dispatch.

The fast path is guarded the same way as the CSI fast paths: handlers
with a vtRaw hook (the inspector) keep receiving per-byte apc_put
actions, and the scalar next() path is unchanged.

Also add benchmark support: a `ghostty-gen +kitty` synthetic generator
emitting well-formed Kitty graphics transmit commands with 4 KiB
random base64 payloads (not valid image data; the corpus exercises
the parsing paths, not image decoding), and a `ghostty-bench
+apc-parser` benchmark that measures the stream -> APC -> Kitty parse
path without image decode/storage.

Benchmarks on a 64 MiB corpus (hyperfine, ReleaseFast, x86_64 Linux,
baseline is identical source with only the fast path disabled):

  apc-parser:               1.061 s -> 43 ms  (~25x)
  terminal-stream (kitty):  1.163 s -> 72 ms  (~16x)
  terminal-stream (ascii):  no change

The ascii case was verified with retired instruction counts (perf
stat, pinned to one core) since wall time on the test machine has
4-7 ms of noise: 988,030,458 vs 988,045,833 instructions (+0.0016%),
a fixed startup-size delta; the ground-state hot loop never reaches
the new branch.

src/benchmark/cli.zig

@@ -6,6 +6,7 @@ const cli = @import("../cli.zig");
 /// benchmarks. View docs for each individual one in the predictably
 /// named files.
 pub const Action = enum {
+    @"apc-parser",
     @"codepoint-width",
     @"grapheme-break",
     @"page-compression",
@@ -26,6 +27,7 @@ pub const Action = enum {
     /// See TerminalStream for an example.
     pub fn Struct(comptime action: Action) type {
         return switch (action) {
+            .@"apc-parser" => @import("ApcParser.zig"),
             .@"screen-clone" => @import("ScreenClone.zig"),
             .@"page-compression" => @import("PageCompression.zig"),
             .@"scrollback-compression" => @import("ScrollbackCompression.zig"),