parser_.opts.python_decode_obj_api_strings doesn't apply for vector of strings

[dshekter]

When a vector of strings is used, the generated code does not correctly decode into a string type and instead leaves the data as bytes (which is counter to the type hint).

Schema:

table test {
    vec_of_string: [string];
    single_string: string;
}

root_type test;

compiled with: ./build/flatc --python --python-version 3.12 --python-typing --gen-object-api --python-decode-obj-api-strings -o /tmp/blah/ strings.fbs

resulting code:

class testT(object):

    # testT
    def __init__(self):
        self.vecOfString = None  # type: Optional[List[Optional[str]]]
        self.singleString = None  # type: Optional[str]
...

This is correct, though I would question if it shouldn't be Optional[List[str]] instead. (since the .pyi generates typing.List[str] not str | None like the single case)

    # testT
    def _UnPack(self, test):
        if test is None:
            return
        if not test.VecOfStringIsNone():
            self.vecOfString = []
            for i in range(test.VecOfStringLength()):
                self.vecOfString.append(test.VecOfString(i))
        self.singleString = test.SingleString()
        if self.singleString is not None:
            self.singleString = self.singleString.decode('utf-8')

This is incorrect. self.vecOfString.append(test.VecOfString(i)) should be self.vecOfString.append(test.VecOfString(i)).decode('utf-8'). If it's actually optional, I guess it should do a None check first. But regardless it should be decoding to match the type hint.