Uniformize usage() and extra_usage() message ending for commands helper. (#8268)

# Description

Working on uniformizing the ending messages regarding methods usage()
and extra_usage(). This is related to the issue
https://github.com/nushell/nushell/issues/5066 after discussing it with
@jntrnr

# User-Facing Changes

None.

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/src/conversions/fill.rs

@@ -37,7 +37,7 @@ impl Command for Fill {
     }
 
     fn usage(&self) -> &str {
-        "Fill and Align"
+        "Fill and Align."
     }
 
     fn signature(&self) -> nu_protocol::Signature {

crates/nu-command/src/conversions/fmt.rs

@@ -15,7 +15,7 @@ impl Command for Fmt {
     }
 
     fn usage(&self) -> &str {
-        "Format a number"
+        "Format a number."
     }
 
     fn signature(&self) -> nu_protocol::Signature {

crates/nu-command/src/conversions/into/binary.rs

@@ -36,7 +36,7 @@ impl Command for SubCommand {
     }
 
     fn usage(&self) -> &str {
-        "Convert value to a binary primitive"
+        "Convert value to a binary primitive."
     }
 
     fn search_terms(&self) -> Vec<&str> {

crates/nu-command/src/conversions/into/bool.rs

@@ -32,7 +32,7 @@ impl Command for SubCommand {
     }
 
     fn usage(&self) -> &str {
-        "Convert value to boolean"
+        "Convert value to boolean."
     }
 
     fn search_terms(&self) -> Vec<&str> {

crates/nu-command/src/conversions/into/datetime.rs

@@ -139,7 +139,7 @@ impl Command for SubCommand {
     }
 
     fn usage(&self) -> &str {
-        "Convert text into a datetime"
+        "Convert text into a datetime."
     }
 
     fn search_terms(&self) -> Vec<&str> {

crates/nu-command/src/conversions/into/decimal.rs

@@ -28,7 +28,7 @@ impl Command for SubCommand {
     }
 
     fn usage(&self) -> &str {
-        "Convert text into a decimal"
+        "Convert text into a decimal."
     }
 
     fn search_terms(&self) -> Vec<&str> {

crates/nu-command/src/conversions/into/duration.rs

@@ -39,7 +39,7 @@ impl Command for SubCommand {
     }
 
     fn usage(&self) -> &str {
-        "Convert value to duration"
+        "Convert value to duration."
     }
 
     fn extra_usage(&self) -> &str {

crates/nu-command/src/conversions/into/filesize.rs

@@ -31,7 +31,7 @@ impl Command for SubCommand {
     }
 
     fn usage(&self) -> &str {
-        "Convert value to filesize"
+        "Convert value to filesize."
     }
 
     fn search_terms(&self) -> Vec<&str> {

crates/nu-command/src/conversions/into/int.rs

@@ -49,7 +49,7 @@ impl Command for SubCommand {
     }
 
     fn usage(&self) -> &str {
-        "Convert value to integer"
+        "Convert value to integer."
     }
 
     fn search_terms(&self) -> Vec<&str> {

crates/nu-command/src/conversions/into/record.rs

@@ -27,7 +27,7 @@ impl Command for SubCommand {
     }
 
     fn usage(&self) -> &str {
-        "Convert value to record"
+        "Convert value to record."
     }
 
     fn search_terms(&self) -> Vec<&str> {

crates/nu-command/src/conversions/into/string.rs

@@ -57,7 +57,7 @@ impl Command for SubCommand {
     }
 
     fn usage(&self) -> &str {
-        "Convert value to string"
+        "Convert value to string."
     }
 
     fn search_terms(&self) -> Vec<&str> {