Ensure that command usage starts uppercase and ends period (#11278)

# Description

This repeats #8268 to make all command usage strings start with an
uppercase letter and end with a period per #5056

Adds a test to ensure that commands won't regress

Part of #5066

# User-Facing Changes

Command usage is now consistent

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

Automatic documentation updates

crates/nu-command/src/hash/generic_digest.rs

@@ -24,7 +24,7 @@ impl<D: HashDigest> Default for GenericDigest<D> {
     fn default() -> Self {
         Self {
             name: format!("hash {}", D::name()),
-            usage: format!("Hash a value using the {} hash algorithm", D::name()),
+            usage: format!("Hash a value using the {} hash algorithm.", D::name()),
             phantom: PhantomData,
         }
     }