Fix default argument value type checking (#10460)

# Description
Fix type checking in arguments default values not adhering to subtyping
rules
Currently following examples produce a parse error:
```nu
def test [ --qwe: record<a: int> = {a: 1 b: 1} ] { }
def test [ --qwe: list<any> = [ 1 2 3 ] ] { }
```
despite types matching. Type equality check is replaced with subtyping
check and everything parses fine:
# User-Facing Changes
Default values of flag arguments type checking behavior is in line with
`let` statements

crates/nu-parser/src/parser.rs

@@ -3838,7 +3838,7 @@ pub fn parse_signature_helper(working_set: &mut StateWorkingSet, span: Span) ->
                                                 }
                                             }
                                             t => {
-                                                if t != &expression_ty {
+                                                if !type_compatible(t, &expression_ty) {
                                                     working_set.error(
                                                         ParseError::AssignmentMismatch(
                                                             "Default value is the wrong type"