Missing HVP (CSI f) support — treated as unhandled instead of CUP

[maurerdietmar]

Missing HVP (CSI f) support — treated as unhandled instead of CUP

Summary

The vt100 parser handles CUP (CSI Ps ; Ps H) but does not handle its
equivalent HVP (CSI Ps ; Ps f). Per ECMA-48 §8.3.63, HVP (Horizontal
and Vertical Position) is functionally identical to CUP (Cursor Position)
— both set the cursor to the specified row and column. The parser
currently sends HVP to the unhandled_csi callback instead.

Affected code

In src/perform.rs, the csi_dispatch match for no-intermediate CSI
sequences handles 'H' but not 'f':

'H' => self.screen.cup(canonicalize_params_2(params, 1, 1)),

Suggested fix

Add 'f' to the existing 'H' arm:

'H' | 'f' => self.screen.cup(canonicalize_params_2(params, 1, 1)),

Real-world impact

Applications that use HVP include mpv with --vo=sixel, which emits
ESC [ <row> ; <col> f to position the cursor before drawing each Sixel
frame. Without this, cursor positioning is silently ignored and image
placement breaks.

Reference

• ECMA-48 5th Edition, §8.3.63 (HVP) and §8.3.21 (CUP)
• https://invisible-island.net/xterm/ctlseqs/ctlseqs.html — lists both
  CSI Ps ; Ps H and CSI Ps ; Ps f as "Cursor Position"

[rramphal]

Two open PRs implement this: #34 and #36. Both route f to the existing cup() handler.