feat: Implement conversion for level types

Implement `From<Verbosity>` for `LevelFilter` and `Option<Level>` for
both `log` and `tracing` crates.

This makes it possible to just directly set the log filter:

E.g.:
```rust
env_logger::Builder::new().filter_level(cli.verbosity.into()).init();
// or
tracing_subscriber::fmt().with_max_level(cli.verbosity).init();
```

examples/log.rs

@@ -5,14 +5,14 @@ use clap_verbosity_flag::Verbosity;
 #[derive(Debug, Parser)]
 struct Cli {
     #[command(flatten)]
-    verbose: Verbosity,
+    verbosity: Verbosity,
 }
 
 fn main() {
     let cli = Cli::parse();
 
     env_logger::Builder::new()
-        .filter_level(cli.verbose.log_level_filter())
+        .filter_level(cli.verbosity.into())
         .init();
 
     log::error!("Engines exploded");

examples/tracing.rs

@@ -5,14 +5,14 @@ use clap_verbosity_flag::Verbosity;
 #[derive(Debug, Parser)]
 struct Cli {
     #[command(flatten)]
-    verbose: Verbosity,
+    verbosity: Verbosity,
 }
 
 fn main() {
     let cli = Cli::parse();
 
     tracing_subscriber::fmt()
-        .with_max_level(cli.verbose.tracing_level_filter())
+        .with_max_level(cli.verbosity)
         .init();
 
     tracing::error!("Engines exploded");

src/log.rs

@@ -3,7 +3,7 @@
 // information.
 pub use log::{Level, LevelFilter};
 
-use crate::VerbosityFilter;
+use crate::{LogLevel, Verbosity, VerbosityFilter};
 
 impl From<VerbosityFilter> for LevelFilter {
     fn from(filter: VerbosityFilter) -> Self {
@@ -57,6 +57,18 @@ impl From<Option<Level>> for VerbosityFilter {
     }
 }
 
+impl<L: LogLevel> From<Verbosity<L>> for LevelFilter {
+    fn from(v: Verbosity<L>) -> Self {
+        v.log_level_filter()
+    }
+}
+
+impl<L: LogLevel> From<Verbosity<L>> for Option<Level> {
+    fn from(v: Verbosity<L>) -> Self {
+        v.log_level()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -88,4 +100,46 @@ mod tests {
         assert_eq!(v.log_level(), Some(Level::Trace));
         assert_eq!(v.log_level_filter(), LevelFilter::Trace);
     }
+
+    #[test]
+    fn into_opt_level() {
+        let v = Verbosity::<OffLevel>::default();
+        assert_eq!(Option::<Level>::from(v), None);
+
+        let v = Verbosity::<ErrorLevel>::default();
+        assert_eq!(Option::<Level>::from(v), Some(Level::Error));
+
+        let v = Verbosity::<WarnLevel>::default();
+        assert_eq!(Option::<Level>::from(v), Some(Level::Warn));
+
+        let v = Verbosity::<InfoLevel>::default();
+        assert_eq!(Option::<Level>::from(v), Some(Level::Info));
+
+        let v = Verbosity::<DebugLevel>::default();
+        assert_eq!(Option::<Level>::from(v), Some(Level::Debug));
+
+        let v = Verbosity::<TraceLevel>::default();
+        assert_eq!(Option::<Level>::from(v), Some(Level::Trace));
+    }
+
+    #[test]
+    fn into_level_filter() {
+        let v = Verbosity::<OffLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::Off);
+
+        let v = Verbosity::<ErrorLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::Error);
+
+        let v = Verbosity::<WarnLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::Warn);
+
+        let v = Verbosity::<InfoLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::Info);
+
+        let v = Verbosity::<DebugLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::Debug);
+
+        let v = Verbosity::<TraceLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::Trace);
+    }
 }

src/tracing.rs

@@ -3,7 +3,7 @@
 // more information.
 pub use tracing_core::{Level, LevelFilter};
 
-use crate::VerbosityFilter;
+use crate::{LogLevel, Verbosity, VerbosityFilter};
 
 impl From<VerbosityFilter> for LevelFilter {
     fn from(filter: VerbosityFilter) -> Self {
@@ -57,6 +57,18 @@ impl From<Option<Level>> for VerbosityFilter {
     }
 }
 
+impl<L: LogLevel> From<Verbosity<L>> for LevelFilter {
+    fn from(v: Verbosity<L>) -> Self {
+        v.tracing_level_filter()
+    }
+}
+
+impl<L: LogLevel> From<Verbosity<L>> for Option<Level> {
+    fn from(v: Verbosity<L>) -> Self {
+        v.tracing_level()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -88,4 +100,46 @@ mod tests {
         assert_eq!(v.tracing_level(), Some(Level::TRACE));
         assert_eq!(v.tracing_level_filter(), LevelFilter::TRACE);
     }
+
+    #[test]
+    fn into_opt_level() {
+        let v = Verbosity::<OffLevel>::default();
+        assert_eq!(Option::<Level>::from(v), None);
+
+        let v = Verbosity::<ErrorLevel>::default();
+        assert_eq!(Option::<Level>::from(v), Some(Level::ERROR));
+
+        let v = Verbosity::<WarnLevel>::default();
+        assert_eq!(Option::<Level>::from(v), Some(Level::WARN));
+
+        let v = Verbosity::<InfoLevel>::default();
+        assert_eq!(Option::<Level>::from(v), Some(Level::INFO));
+
+        let v = Verbosity::<DebugLevel>::default();
+        assert_eq!(Option::<Level>::from(v), Some(Level::DEBUG));
+
+        let v = Verbosity::<TraceLevel>::default();
+        assert_eq!(Option::<Level>::from(v), Some(Level::TRACE));
+    }
+
+    #[test]
+    fn into_level_filter() {
+        let v = Verbosity::<OffLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::OFF);
+
+        let v = Verbosity::<ErrorLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::ERROR);
+
+        let v = Verbosity::<WarnLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::WARN);
+
+        let v = Verbosity::<InfoLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::INFO);
+
+        let v = Verbosity::<DebugLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::DEBUG);
+
+        let v = Verbosity::<TraceLevel>::default();
+        assert_eq!(LevelFilter::from(v), LevelFilter::TRACE);
+    }
 }