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/bytes/at.rs

@@ -57,7 +57,7 @@ impl Command for BytesAt {
     }
 
     fn usage(&self) -> &str {
-        "Get bytes defined by a range"
+        "Get bytes defined by a range."
     }
 
     fn search_terms(&self) -> Vec<&str> {