chore: move c-api and benches to edition 2024

Edition 2024 makes #[no_mangle] an unsafe attribute, so all 53 exported
c-api symbols become #[unsafe(no_mangle)]. Verified with the gcc
AddressSanitizer pass over test.c.

testing-tools/ttf-fuzz is left on edition 2018 deliberately: it has not
compiled since Face::parse started returning Result in 0.8.0, and it is
superseded by the cargo-fuzz crate in #179.

Author: Goldziher

benches/Cargo.toml

@@ -1,7 +1,8 @@
 [package]
 name = "benchmarks"
 version = "0.1.0"
-edition = "2018"
+edition = "2024"
+rust-version = "1.88.0"
 
 [dependencies]
 bencher = "0.1"

c-api/Cargo.toml

@@ -8,7 +8,8 @@ authors = [
     "خالد حسني (Khaled Hosny) <khaled@aliftype.com>"
 ]
 license = "MIT"
-edition = "2018"
+edition = "2024"
+rust-version = "1.88.0"
 
 [lib]
 name = "ttfparser"