GUIModel: new dataclass-based API, support pydantic and python dataclasses

[tlambert03]

this will supersede #379 and #318 docs to follow

from magicgui import GUIModel, Field
from datetime import date

class MyModel(GUIModel):
    name: str
    age: int
    married: bool
    salary: float = Field(..., ge=0, le=999999)
    birthday: date

obj = MyModel(
    name="Frank", age=55, married=True, salary=100000, birthday=date(1980, 1, 1)
)
obj.gui.show(run=True)

obj.age = 42
assert obj.age == obj.gui.age.value == 42

[codecov[bot]]

Codecov Report

Merging #446 (0667d8a) into main (e803f97) will increase coverage by 0.38%. The diff coverage is 99.23%.

@@            Coverage Diff             @@
##             main     #446      +/-   ##
==========================================
+ Coverage   89.02%   89.40%   +0.38%     
==========================================
  Files          30       31       +1     
  Lines        3953     4057     +104     
==========================================
+ Hits         3519     3627     +108     
+ Misses        434      430       -4     

Impacted Files	Coverage Δ
magicgui/type_map.py	95.75% <95.65%> (+0.16%)	:arrow_up:
magicgui/_guimodel.py	100.00% <100.00%> (ø)
magicgui/widgets/_bases/container_widget.py	93.15% <100.00%> (+0.03%)	:arrow_up:
magicgui/widgets/_concrete.py	86.73% <100.00%> (ø)
magicgui/backends/_qtpy/widgets.py	87.42% <0.00%> (+0.47%)	:arrow_up:

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[tlambert03]

closing this in favor of #475 ... this PR was going to add pydantic as a dependency, and require using magicgui.GuiModel as a base class. I think we implement something lighter that will also support native dataclasses, attrs, NamedTuple, TypedDict, etc... see #474 for discussion