Implementation of UDF generator

Created by: jassak

Introduces:

• A function generate_udf to be called with parameters:

  func_name: str,
  udf_name: str,
  input_tables: list[dict],
  loopback_tables: list[dict],
  literalparams: dict,

  This method produces a string with the corresponding SQL UDF definition.
• A decorator udf to be used with all functions which will be used as MonetDB Python UDFs. These functions have to be type annotated with a number of allowed types (see below).
• A series of Types to use with UDFs. Namelly:
  • TableT, representing a relational table in the DB, passed as an argument to a UDF.
  • TensorT, representing a n-dimensional tensor, stored as a table in the DB, also passed as an argument.
  • LoopbackTableT, a table stored in the DB but loaded in the UDF as a loopback call.
  • LiteralParameterT, a scalar parameter not stored in the DB, hard-coded as a literal in the UDF body.
  • ScalarT used only for scalar return types.