PR: Use AsyncDispatcher as class decorator (API)

[hlouzada]

Description of Changes

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)

• Included a screenshot or animation (if affecting the UI, see Licecap)

Fix typings issue with AsyncDispatcher, refactor to use as decorator and add minor improvements on logic for performace.

New Usage:

Non-Blocking usage (returns a concurrent Future):

@AsyncDispatcher()
async def my_coroutine(...):
    ...

future = my_coroutine(...)  # Non-blocking call

result = future.result()  # Blocking call

Blocking usage (returns the result):

@AsyncDispatcher(early_return=False)
async def my_coroutine(...):
    ...

result = my_coroutine(...)  # Blocking call

Coroutine usage (returns an awaitable Future):

@AsyncDispatcher(return_awaitable=True)
async def my_coroutine(...):
    ...

result = await my_coroutine(...)  # Wait for the result to be ready

Affirmation

By submitting this Pull Request or typing my (user)name below,
I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

I certify the above statement is true and correct: @hlouzada