Update internal use of decimal to float (#10333)

# Description
We made the decision that our floating point type should be referred to
as `float` over `decimal`.
Commands were updated by #9979 and #10320

Now make the internal codebase consistent in referring to this data type
as `float`.

Work for #10332

# User-Facing Changes

`decimal` has been removed as a type name/symbol. 

Instead of 
```nushell
def foo [bar: decimal] decimal -> decimal {}
```
use 
```nushell
def foo [bar: float] float -> float {}
```

Potential effect of `SyntaxShape`'s `Display` implementation now also
referring to `float` instead of `decimal`

# Details
- Rename `SyntaxShape::Decimal` to `Float`
- Update `Display for SyntaxShape` to `float`
- Update error message + fn name in dataframe code
- Fix docs in command examples
- Rename tests that are float specific
- Update doccomment on `SyntaxShape`
- Update comment in script

# Tests + Formatting
Updates the names of some tests

crates/nu-command/tests/commands/math/mod.rs

@@ -117,7 +117,7 @@ fn error_zero_division_int_int() {
 }
 
 #[test]
-fn error_zero_division_decimal_int() {
+fn error_zero_division_float_int() {
     let actual = nu!(pipeline(
         r#"
             1.0 / 0
@@ -128,7 +128,7 @@ fn error_zero_division_decimal_int() {
 }
 
 #[test]
-fn error_zero_division_int_decimal() {
+fn error_zero_division_int_float() {
     let actual = nu!(pipeline(
         r#"
             1 / 0.0
@@ -139,7 +139,7 @@ fn error_zero_division_int_decimal() {
 }
 
 #[test]
-fn error_zero_division_decimal_decimal() {
+fn error_zero_division_float_float() {
     let actual = nu!(pipeline(
         r#"
             1.0 / 0.0
@@ -194,7 +194,7 @@ fn error_zero_floor_division_int_int() {
 }
 
 #[test]
-fn error_zero_floor_division_decimal_int() {
+fn error_zero_floor_division_float_int() {
     let actual = nu!(pipeline(
         r#"
             1.0 // 0
@@ -205,7 +205,7 @@ fn error_zero_floor_division_decimal_int() {
 }
 
 #[test]
-fn error_zero_floor_division_int_decimal() {
+fn error_zero_floor_division_int_float() {
     let actual = nu!(pipeline(
         r#"
             1 // 0.0
@@ -216,7 +216,7 @@ fn error_zero_floor_division_int_decimal() {
 }
 
 #[test]
-fn error_zero_floor_division_decimal_decimal() {
+fn error_zero_floor_division_float_float() {
     let actual = nu!(pipeline(
         r#"
             1.0 // 0.0