pydantic `BaseModel` also has custom `__eq__`

[cjw296]

...so if you have one that has a dataframe as an attribute, then testfixures handling of that never gets a chance to stop the crash.

Do we:

• Add handling for PyDantic explicitly?
• Figure out something more generic where class has custom __eq__?
• Just ignore_eq globally

[cjw296]

Replace OrmBox object in "Custom containers and ignore_eq" example with pydantic containing dataframe to make it real

[cjw296]

Can we make use of this principle of strict? Seems a bit shonky...

2. It stops trusting __eq__ (qualified_equals returns False under strict): for two values of the same type it always inspects their contents instead of short-circuiting on x == y.

I verified the behaviour rather than inferring it. By default these all compare equal, and strict=True flags each: