Three failure modes shared the same root cause on the StdinBuffer.process
hot path — unbounded synchronous work in a single call.
- `StdinBuffer.extractCompleteSequences` grew each escape candidate one code
unit at a time and re-tested every prefix, so a malformed CSI/OSC/DCS/APC
streamed across chunks re-inspected the accumulated buffer on every
`process()` call (issue A). Replaced the grow-and-recheck loop with a
single linear scan bounded by a per-type cap (CSI 4 KiB, OSC/DCS/APC 16
MiB) and a resume-search offset carried on `StdinBuffer` so a legit
chunked OSC 5522 image paste stays O(total) instead of O(total²).
- `BracketedPasteHandler` had no cap or timeout: a caller that bypassed
StdinBuffer (fed the start marker with no end marker) grew `#buffer`
forever (issue B, defense in depth). Added an optional `byteLimit` option
(default 64 MiB) that aborts paste mode and delivers accumulated bytes as
`pasteContent`, mirroring `StdinBuffer#abortPaste`.
- The `ProcessTerminal` data handler ran six always-executed escape-probe
regex tests per `data` event; a 100 KB non-bracketed paste (terminal
without DEC 2004 support) turned into ~600K regex executions (issue C).
Added a fast path that forwards non-ESC sequences straight to the input
handler when no reassembly buffer is holding state.
Verified with new stdin-buffer + bracketed-paste tests plus empirical
repros: a streamed 1 MiB malformed CSI drops from ~4300 ms to ~50 ms of
synchronous work, and a 1 MiB chunked OSC 5522 payload drops from ~6800 ms
to ~25 ms.
Fixes#4073
