Debloat the binary by using less AsRef arguments

Using `impl AsRef<str>` as the argument instead of `&str` makes it
possible to call the function with `&str`, `String` and other types
that implement `AsRef` trait.

The cost of it is that compiled binary contains mulitple versions of
the same function, one for each variant of types. If function contains
multiple generic `impl AsRef` arguments, the number of versions possibly
compiled into binary grows exponentially with the number of arguments.

Simple way to avoid it is to call `.as_ref()` on the caller side to
convert the argument to `&str`. In most cases even adding a `&` and
relying on `Deref` coercion is sufficient.

This patch changes many functions that accepted `impl AsRef<str>` and
`impl AsRef<Path>` to accept `&str` and `&Path` instead.

In some places `.clone()` calls are removed. Calling `.clone()` on
`String` and passing `String` to a function accepting `impl
AsRef<str>` is completely unnecessary as `&str` reference could be
passed instead. There is no clippy warning against it yet, but
changing argument type to `&str` allowed to find these cases.

The result of debloating is not impressive, several hundred kilobytes
are saved, which is about 3% of the `.so` binary, but the code is
cleaner too.

src/message.rs

@@ -2034,7 +2034,7 @@ pub(crate) async fn rfc724_mid_exists(
 pub async fn update_server_uid(
     context: &Context,
     rfc724_mid: &str,
-    server_folder: impl AsRef<str>,
+    server_folder: &str,
     server_uid: u32,
 ) {
     match context
@@ -2042,7 +2042,7 @@ pub async fn update_server_uid(
         .execute(
             "UPDATE msgs SET server_folder=?, server_uid=? \
              WHERE rfc724_mid=?",
-            paramsv![server_folder.as_ref(), server_uid, rfc724_mid],
+            paramsv![server_folder, server_uid, rfc724_mid],
         )
         .await
     {