Add types to generated adapter read method

[Scowley4]

Generated read method for adapters is currently missing types on two local variables (numOfFields and fields). This PR would add those types to the generated code.

[themisir]

Don't get me wrong but, this is opinionated change, some linter rules might require removing type annotations in above cases while some might want them to be there. In any case I would suggest ignoring linting on generated files if that's the case with you.

[Scowley4]

@themisir Oh, that's interesting -- hadn't thought of that. I'm still pretty new to dart and I thought putting types in these places was "the standard".

You're probably right that I should ignore the generated files in my linter.

[themisir]

Yeah don't worry, it's alright. Dart linter is somewhat configurable using analyzer_options.yaml file. So some projects prefer all explicit type annotations while other ones prefer to not annotate types on obvious cases, I don't remember exact rule names but saw both rules used in different projects. I might be wrong tho, I haven't worked on dart project on last 3-4 months.