[ENH] Remove redundant method overrides in Skellam and FDist

[ANANYA542]

Description

Both Skellam and FDist distributions extend _ScipyAdapter and implement _get_scipy_param() correctly. However, they both manually overrode _pmf / _pdf, _cdf, _ppf, _mean, and _var with logic that is completely identical to what the adapter already provides natively.
For example, Skellam._pmf manually does:
For example, Skellam._pmf manually does:
def _pmf(self, x):
mu1 = self._bc_params["mu1"]
mu2 = self._bc_params["mu2"]
return skellam.pmf(x, mu1, mu2)
But _ScipyAdapter._pmf already does exactly this via _get_scipy_param() . Since Skellam._get_scipy_param() returns [mu1, mu2], {}, both paths are mathematically identical. These overrides add roughly 25 redundant lines per file with no functional difference whatsoever. This commit removes those redundant methods, letting the _ScipyAdapter
base class handle them as designed, which significantly reduces code duplication. I validated this locally by removing the overrides and confirming identical outputs before and after.

Reference Issues/PRs

Fixes #944

What does this implement/fix? Explain your changes.

This PR deletes redundant core distribution method overrides from skellam.py and f.py (or f_dist.py), allowing them to cleanly inherit the exact same behavior from _ScipyAdapter.

Does your contribution introduce a new dependency? If yes, which one?

no

What should a reviewer concentrate their feedback on?

1. Confirming that the removed methods were indeed exactly duplicating the native _ScipyAdapter behavior.
2. Verifying the CI tests still pass successfully using the inherited adapter methods.

Did you add any tests for the change?

No new tests are required because the existing distribution tests in the CI pipeline automatically verify that mean, var,pdf/
pmf, cdf and ppf work correctly, ensuring no functionality is broken by relying on the base class.

Any other comments?

The screenshot for the fix has been attatched

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[ANANYA542]

@fkiraly -if you could review this pr and let me know if some changes or explanation under the same are required