docs: Miscellaneous doc fixes in attribute + unit tests

[austinvalle]

Just some cleaning up I found while working on something else.

---

FYI, for the unit tests being uncommented, they were originally failing because collection types with missing element types are considered invalid, and thus not equal:

terraform-plugin-framework/types/basetypes/list_type.go

Lines 112 to 115 in 91edd79

	// Preserve prior ElemType nil check behavior
	if l.ElementType().Equal(missingType{}) {
	return false
	}

Since all these custom type tests were embedding the underlying collection type, the element type was nil, thus failing the cmp.Diff in all the tests with a confusing diff 😆

--- FAIL: TestMapNestedAttributeGetType (0.00s)
    --- FAIL: TestMapNestedAttributeGetType/custom-type (0.00s)
        /Users/austin.valle/code/terraform-plugin-framework/resource/schema/map_nested_attribute_test.go:411: unexpected difference:   testtypes.MapType(
            - 	{},
            + 	{},
              )

The int64/int32/float64/float32/object unit tests were never failing, but likely just commented out on accident 👍🏻

[austinvalle]

Also contains the linter fixes for go 1.23 😆

Edit: Framework linting fixes are in main now!