perf: inline public getters/setters, and use non-generic inner functions

To reduce compile-times and avoid some overhead to binary size, this will modify some of our
generic functions to use non-generic inner functions where possible. The inner functions are
marked carefully with `#[inline(never)]` to prevent being inlined by LLVM at their callsites

While looking for generic functions to optimize, I have also taken the opportunity to annotate
public non-generic getters and setters with `#[inline]` to ensure that LLVM will inline them
across crate boundaries. By default, only generic functions are automatically inlined, and
only when enabling fat LTO are constant functions reliably inlined across crate boundaries.

cosmic-config/src/dbus.rs

@@ -20,6 +20,7 @@ pub struct Watcher {
 
 impl Deref for Watcher {
     type Target = ConfigProxy<'static>;
+    #[inline]
     fn deref(&self) -> &Self::Target {
         &self.proxy
     }

cosmic-config/src/lib.rs

@@ -40,6 +40,7 @@ pub enum Error {
 }
 
 impl fmt::Display for Error {
+    #[cold]
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
             Self::AtomicWrites(err) => err.fmt(f),
@@ -61,6 +62,7 @@ impl Error {
     /// Whether the reason for the missing config is caused by an error.
     ///
     /// Useful for determining if it is appropriate to log as an error.
+    #[inline]
     pub fn is_err(&self) -> bool {
         !matches!(self, Self::NoConfigDirectory | Self::NotFound)
     }
@@ -134,11 +136,6 @@ fn sanitize_name(name: &str) -> Result<&Path, Error> {
 }
 
 impl Config {
-    /// Get the config for the libcosmic toolkit
-    pub fn libcosmic() -> Result<Self, Error> {
-        Self::new("com.system76.libcosmic", 1)
-    }
-
     /// Get a system config for the given name and config version
     pub fn system(name: &str, version: u64) -> Result<Self, Error> {
         let path = sanitize_name(name)?.join(format!("v{version}"));
@@ -235,6 +232,7 @@ impl Config {
     }
 
     // Start a transaction (to set multiple configs at the same time)
+    #[inline]
     pub fn transaction(&self) -> ConfigTransaction {
         ConfigTransaction {
             config: self,
@@ -368,7 +366,7 @@ pub struct ConfigTransaction<'a> {
     updates: Mutex<Vec<(PathBuf, String)>>,
 }
 
-impl<'a> ConfigTransaction<'a> {
+impl ConfigTransaction<'_> {
     /// Apply all pending changes from ConfigTransaction
     //TODO: apply all changes at once
     pub fn commit(self) -> Result<(), Error> {
@@ -386,7 +384,7 @@ impl<'a> ConfigTransaction<'a> {
 
 // Setting any setting in this way will do one transaction for all settings
 // when commit finishes that transaction
-impl<'a> ConfigSet for ConfigTransaction<'a> {
+impl ConfigSet for ConfigTransaction<'_> {
     fn set<T: Serialize>(&self, key: &str, value: T) -> Result<(), Error> {
         //TODO: sanitize key (no slashes, cannot be . or ..)
         let key_path = self.config.key_path(key)?;

cosmic-config/src/subscription.rs

@@ -16,6 +16,7 @@ pub enum ConfigUpdate<T> {
     Failed,
 }
 
+#[cold]
 pub fn config_subscription<
     I: 'static + Copy + Send + Sync + Hash,
     T: 'static + Send + Sync + PartialEq + Clone + CosmicConfigEntry,
@@ -27,6 +28,7 @@ pub fn config_subscription<
     iced_futures::Subscription::run_with_id(id, watcher_stream(config_id, config_version, false))
 }
 
+#[cold]
 pub fn config_state_subscription<
     I: 'static + Copy + Send + Sync + Hash,
     T: 'static + Send + Sync + PartialEq + Clone + CosmicConfigEntry,