add support for metadata comments

[prabirshrestha]

For example one could set metadata comments on fields or types to provide a lot more concrete information such as sql types or char limit or other hints.

type User {
  id:      UUID
  @sql('nvarchar(1600) NOT NULL')
  name:    String
  email:   Option<Email>
  roles:   List<Role>
  address: Address
}

this could just be @key(value) and could be anything.

might be somethign similar to golang comments but this could be super long.

type User struct {
    id: string `json:"tagada,omitempty"`
}

this might not be good as it could be too long.

type User struct {
    //# sql: nvarchar(255)
    id: string
}

type User struct {
    //@ sql("nvarchar(255)")
    id: string
}

this is more to add extra metadata as comments that one could try to parse into structed data for UIs if needed to show better diagrams or help llm understand and generate code.