add constant-expression string utils

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

src/api/Cargo.toml

@@ -41,6 +41,7 @@ bytes.workspace = true
 conduit-core.workspace = true
 conduit-database.workspace = true
 conduit-service.workspace = true
+const-str.workspace = true
 futures-util.workspace = true
 hmac.workspace = true
 http.workspace = true