[Python] Enhance object API __init__ with typed keyword arguments

[crackcomm]

This commit significantly improves the developer experience for the Python Object-Based API by overhauling the generated __init__ method for T-suffixed classes.

Previously, T objects had to be instantiated with an empty constructor, and their fields had to be populated manually one by one. This was verbose and not idiomatic Python.

This change modifies the Python code generator (GenInitialize) to produce __init__ methods that are:

1. Keyword-Argument-Friendly: The constructor now accepts all table/struct fields as keyword arguments, allowing for concise, single-line object creation.

2. Fully Typed: The signature of the __init__ method is now annotated with Python type hints. This provides immediate benefits for static analysis tools (like Mypy) and IDEs, enabling better autocompletion and type checking.

3. Correctly Optional: The generator now correctly wraps types in Optional[...] if their default value is None. This applies to strings, vectors, and other nullable fields, ensuring strict type safety.

The new approach remains fully backward-compatible, as all arguments have default values. Existing code that uses the empty constructor will continue to work without modification.

Example of a Generated __init__

Before:

class KeyValueT(object):
    def __init__(self):
        self.key = None  # type: str
        self.value = None  # type: str

After:

class KeyValueT(object):
    def __init__(self, key: Optional[str] = None, value: Optional[str] = None):
        self.key = key
        self.value = value

Example of User Code

Before:

# Old, verbose way
kv = KeyValueT()
kv.key = "instrument"
kv.value = "EUR/USD"

After:

# New, Pythonic way
kv = KeyValueT(key="instrument", value="EUR/USD")

[fliiiix]

Nice, but im almost certain this will break Python 2 support

File "script.py", line 2
    def __init__(self, key: Optional[str] = None, value: Optional[str] = None):
                          ^
SyntaxError: invalid syntax

Some guarding against that would be probably useful version_.major == 3

[crackcomm]

The code was generated with ./tests/PythonTest.sh, I guess it's missing the flag from #8551? I used scripts/generate_code.py instead.

[fliiiix]

I guess it's missing the flag from #8551?

I guess this flag should not be part of scripts/generate_code.py? and maybe it should have a test

[fliiiix]

@aardappel I just tested this and it looks good to me 👍 if @akb825 has no more comments i guess this could be merged?

[fliiiix]

@aardappel i guess this can be merged?

[akb825]

@aardappel I just tested this and it looks good to me 👍 if @akb825 has no more comments i guess this could be merged?

Sorry, I forgot to reply earlier, looks good on my end.

[aardappel]

thanks :)