feat(unicode,datastruct): port Unicode tables and data structures

ghostty-unicode: Ghostty computes codepoint properties with the uucode
Zig package (v0.2.0, Unicode 17.0.0). There is no Rust equivalent, so
a trimmed UCD set is vendored in ucd/ and build.rs re-implements
uucode's derivations: cell width rules incl. Ghostty's overrides for
emoji modifiers and Prepend, grapheme break classes with the
compile-time grapheme_break state table, the is_symbol set, and emoji
presentation. Lookups are three array indexes per codepoint. Validated
against the official GraphemeBreakTest.txt.

ghostty-datastruct: split_tree (used for GTK splits; f16 ratios so
rounding and debug diagrams match Zig), circ_buf, lru, cache_table,
blocking_queue, segmented_pool, message_data, comparison,
array_list_collection. intrusive_linked_list is not needed (lru is
index based). lru now reports the evicted (old) key, Zig reported the
new key, which appears to be a bug.

Not yet covered: case_folding_full (needed by input bindings).

Test Plan:
- cargo test -p ghostty-unicode (16) -p ghostty-datastruct (88)
- cargo clippy for both crates with -D warnings

crates/ghostty-unicode/Cargo.toml

@@ -3,9 +3,10 @@ name = "ghostty-unicode"
 version.workspace = true
 edition.workspace = true
 license.workspace = true
+build = "build.rs"
+description = "Unicode properties (width, grapheme break, symbols) matching Ghostty's uucode configuration"
 
 [dependencies]
 
-
 [lints]
 workspace = true