od: Extend physical conversion to integer factors, fix typing

[acolomb]

The Variable.phys property docstring mentions "Non integers will be
passed as is." That is correct, but not reflected in the type hints
for the associated ODVariable.encode_phys() / .decode_phys()
functions. Extend the return / argument type to all possible internal
data types, instead of plain int.

Try factor conversion on all NUMBER_TYPES, where it was previously
limited to INTEGER_TYPES. Only apply rounding in encode_phys() if the
variable's data type is actually integer-based.

Allow integer factors in type hint for ODVariable.factor. There is
nothing wrong with using integer factors to yield integers
when decoding. For encoding, the division may still result in a
float, while the rounding behavior is kept unchanged for integer-typed
variables.

Thus, try to parse integer factors as integers from EDS files, not forcing
to a float.

Related comment first given here: #651 (comment)