v2.4.1—gather all my forces all together rally round

• Fixed up nasty memory leak with NCBLIT_PIXEL. Turns out valgrind doesn't track mmap() by default, a fact of which I was sadly unaware (#2150).
• Support for second generation kitty animation was determined to break down in the presence of multiframe plus wiping/rebuilding. This was fixed, but it led to unacceptable slowdown. I've instead disabled second generation animation support until this is fixed (#2143, #2161).
• Properly synthesize SIGINT and SIGQUIT from kitty keyboard protocol.
• Properly send the kitty keyboard pop directive to the alternate screen when it's being used. Fixes the terminal being left in an unexpected keyboard state on exit on kitty when redirected (#2149).
• ncneofetch now properly extracts the macOS version (#2158).
• Some small fixes and tweaks to plots. The summary number now describes the ongoing slot, so it spins up in e.g. notcurses-demo (#2152).
• Added ncstrwidth_valid() (#2153).

2.4.2 work will hopefully see the new input subsystem completed, plus resolution of some CLI-mode problems seen on macOS.

hack on!