Fix most of `clippy::pedantic`

Part of #7.

This MR has fixed many of the clippy::pedantic lints, in alphabetical order.

Due to the huge refactor involved in the latest commit (49a917ba), the clippy::pedantic lints will be fixed in multiple MRs.

There are no interesting commits, just a lot of code being moved around.

rr_frontend/.cargo/config.toml

@@ -32,21 +32,6 @@ rustflags = [
     "-Aclippy::string_lit_as_bytes",
 
     # clippy::pedantic
-    "-Aclippy::bool_to_int_with_if",
-    "-Aclippy::cast_lossless",
-    "-Aclippy::cloned_instead_of_copied",
-    "-Aclippy::default_trait_access",
-    "-Aclippy::doc_markdown",
-    "-Aclippy::expl_impl_clone_on_copy",
-    "-Aclippy::flat_map_option",
-    "-Aclippy::from_iter_instead_of_collect",
-    "-Aclippy::if_not_else",
-    "-Aclippy::inefficient_to_string",
-    "-Aclippy::items_after_statements",
-    "-Aclippy::manual_let_else",
-    "-Aclippy::manual_string_new",
-    "-Aclippy::map_unwrap_or",
-    "-Aclippy::match_same_arms",
     "-Aclippy::must_use_candidate",
     "-Aclippy::needless_continue",
     "-Aclippy::needless_pass_by_value",