Add type hints / documentation for `mode` argument

[ricardoV94]

Description

As discussed in pymc-devs/pymc#7212 (comment) it's not clear what the signature / type is.

Besides a Mode object there is a set of strings that are allowed:

pytensor/pytensor/compile/mode.py

Lines 484 to 534 in a76172e

	def get_mode(orig_string):
	if orig_string is None:
	string = config.mode
	else:
	string = orig_string
	if not isinstance(string, str):
	return string # it is hopefully already a mode...
	global instantiated_default_mode
	# The default mode is cached. However, config.mode can change
	# If instantiated_default_mode has the right class, use it.
	if orig_string is None and instantiated_default_mode:
	if string in predefined_modes:
	default_mode_class = predefined_modes[string].__class__.__name__
	else:
	default_mode_class = string
	if instantiated_default_mode.__class__.__name__ == default_mode_class:
	return instantiated_default_mode
	if string in ("Mode", "DebugMode", "NanGuardMode"):
	if string == "DebugMode":
	# need to import later to break circular dependency.
	from .debugmode import DebugMode
	# DebugMode use its own linker.
	ret = DebugMode(optimizer=config.optimizer)
	elif string == "NanGuardMode":
	# need to import later to break circular dependency.
	from .nanguardmode import NanGuardMode
	# NanGuardMode use its own linker.
	ret = NanGuardMode(True, True, True, optimizer=config.optimizer)
	else:
	# TODO: Can't we look up the name and invoke it rather than using eval here?
	ret = eval(string + "(linker=config.linker, optimizer=config.optimizer)")
	elif string in predefined_modes:
	ret = predefined_modes[string]
	else:
	raise Exception(f"No predefined mode exist for string: {string}")
	if orig_string is None:
	# Build and cache the default mode
	if config.optimizer_excluding:
	ret = ret.excluding(*config.optimizer_excluding.split(":"))
	if config.optimizer_including:
	ret = ret.including(*config.optimizer_including.split(":"))
	if config.optimizer_requiring:
	ret = ret.requiring(*config.optimizer_requiring.split(":"))
	instantiated_default_mode = ret
	return ret

[OriolAbril]

I have found:

• https://pytensor.readthedocs.io/en/latest/glossary.html#term-Mode
• https://pytensor.readthedocs.io/en/latest/library/compile/mode.html#pytensor.compile.mode.Mode

maybe its better to link to the first one for docstrings?