[NuSkooler]

These are three small fixes to #198 (embedder API) and #199 (CTerm conformance) that I found while moving enig-term onto master. Each is its own commit with its own test, and each test fails without its change.

cargo test -p icy_engine -p icy_parser_core passes, and so do the icy_engine lib tests with --no-default-features. With the feature off, 49 icy_engine integration tests that need the bundled fonts fail, the same 49 as on master. cargo fmt --check is clean, clippy has no new warnings in icy_engine, icy_parser_core or icy_engine_gui (with and without default features), and cargo check --workspace passes.

Let the BGI stroke fonts follow embedded-fonts

The BGI .CHR stroke fonts under palette_screen_buffer/bgi/fonts are not under data/fonts, so #198's embedded-fonts feature missed them: they were still compiled in with include_bytes!, about 125 KB, in a --no-default-features build.

They now go through font_bytes! like the other font data. With the feature off, Font::load(&[]) fails, so instead of unwrapping it the font list falls back to a new Font::empty(), which has no characters and draws nothing.

bgi_fonts_absent_do_not_panic (feature off only) resolves every FontType and checks it is an empty font. I also checked the build: a 48-byte sample from GOTH.CHR, SANS.CHR and BOLD.CHR is in libicy_engine.rlib before the change and gone after it.

Make a dotted ANSI music pause 1.5 times as long as a plain one

A dotted pause was stored as Pause(tempo * length * 2 / 3) and played for 240000 / that ms. The two integer divisions round differently from a dotted note's 360000 / (tempo * length), so at some tempos the pause and the note didn't match: T97 P1. lasted 3750 ms instead of 3711, and T121 P4. 745 ms instead of 743.

MusicAction::Pause now carries a dotted flag like PlayNote, and get_duration handles both the same way. This changes the shape of a public enum, so an embedder matching Pause(len) needs Pause(len, dotted) or Pause(..); the one match in icy_engine_gui is updated. If you'd rather keep Pause(i32) as it is, the other option I saw was storing the duration in ms, which I liked less.

test_dotted_pause_lasts_one_and_a_half_times_as_long checks the T97 and T121 values above, and then for every tempo (32 to 255) and length (1 to 64) that a pause and a note last 240000 / (tempo * length) ms, or 360000 / (tempo * length) dotted. Note durations are unchanged.

Restore the configured music option on RIS

RIS resets the music state that carries over between strings, but not the introducers CSI = Ps M picked. After CSI = 0 M, an ESC c left CSI M and CSI N off for the rest of the session.

AnsiParser now remembers the option set_music_option configured and returns to it on RIS. The three icy_engine call sites that assigned the music_option field directly now call set_music_option, so RIS returns to what they set. The field is still public; its doc points to the setter.

test_ris_restores_the_configured_music_option checks that RIS undoes CSI = 0 M, and that after set_music_option(Banana) and CSI = 2 M, RIS returns to Banana and CSI M is Delete Line again.