feat(csharp): idiomatic C# code generation for scalar types, validators, and defaults

[muhabdulkadir]

Closes #

Summary

Significantly improves the C# code generator to produce idiomatic, type-safe C# from Concerto models. This PR adds DataAnnotations validation attributes, and emits default property initializers.

Changes

• Scalar struct validators
  When a scalar declares a validator (regex, length, range), the Value property is explicitly declared with the corresponding DataAnnotations attribute:

  public readonly record struct SSN(string Value)
  {
      [System.ComponentModel.DataAnnotations.RegularExpression(@"\d{3}-\d{2}-\d{4}", ErrorMessage = "Invalid characters")]
      public string Value { get; init; } = Value;
      ...
  }
  

• Numeric range validators on fields
  Integer, Long, and Double fields with a range validator emit [Range]:

  [System.ComponentModel.DataAnnotations.Range(typeof(int), "1", "100")]
  public int salary { get; set; }
  

  Open bounds (only min or only max declared) fill to the type's natural min/max.

• Default property initializers
  Fields with a default value emit a C# property initializer:

  public string name { get; set; } = "Alice";
  public SSN ssn { get; set; } = new("000-00-00-0000");
  

  For scalar-typed fields, the field-level default takes precedence over the scalar declaration's default.

Author Checklist

• Ensure you provide a DCO sign-off for your commits using the --signoff option of git commit.
• Vital features and changes captured in unit and/or integration tests
• Commits messages follow AP format
• Extend the documentation, if necessary
• Merging to main from fork:branchname

[jamieshorten]

How does an entity/instance deserialise/serialise to this

e.g

namespace org.acme.hr@1.0.0
scalar SSN extends String default="000-00-0000" regex=/\d{3}-\d{2}-\{4}+/

concept Person identified by ssn {
    o SSN ssn
    o String givenName
}

would have an instance like

{
   "$class": "org.acme.hr@1.0.0.Person"
    "ssn" : "000-00-0000",
    "givenName": "Jamie"
}

[muhabdulkadir]

How does an entity/instance deserialise/serialise to this

e.g

namespace org.acme.hr@1.0.0
scalar SSN extends String default="000-00-0000" regex=/\d{3}-\d{2}-\{4}+/

concept Person identified by ssn {
    o SSN ssn
    o String givenName
}

would have an instance like

{
   "$class": "org.acme.hr@1.0.0.Person"
    "ssn" : "000-00-0000",
    "givenName": "Jamie"
}

Thanks! I'd add a converter

[jamieshorten]

we should have a round trip test for serialisation/deserialisation of instances to some generated classes. The metamodel would be one candidate...