feat: add native parsing for xsd:float

[michaeladler]

Summary

Implement native parsing support for xsd:float.
Refactor the parsing logic to use a switch-case structure for better readability and maintainability, replacing the previous if-else chain. Integer and double cases are now handled separately, allowing the use of the most suitable standard library parsing methods. This change also eliminates the use of fmt.Sprintf for float-to-integer checks, improving performance.

Basic example

The n-quads

<http://example.com/Subj1> <http://example.com/prop> "1.1E-1"^^<http://www.w3.org/2001/XMLSchema#float> .

should be converted to the following when using native types:

[
  {
    "@id": "http://example.com/Subj1",
    "http://example.com/prop": [
      { "@value": 0.11 }
    ]
  }
]

Motivation

Consistent behavior. It is counterintuitive that double is converted to a native value while float is not. (Unfortunately, xsd:decimal must not be converted, as required by Test t0018.)

Checks

• Passes make test