add math utils; integrate checked expression macros

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/Cargo.toml

@@ -53,6 +53,7 @@ sha256_media = []
 argon2.workspace = true
 axum.workspace = true
 bytes.workspace = true
+checked_ops.workspace = true
 chrono.workspace = true
 either.workspace = true
 figment.workspace = true