CLN: enforce deprecation of `NDFrame.interpolate` with `ffill/bfill/pad/backfill` methods
xref #53607

enforced deprecation of `NDFrame.interpolate` with `"ffill” / "bfill” / “pad” / “backfill"` methods
Thanks for sticking with this @natmokval!  Thanks @mroeschke for helping me with this PR. Enforcing this deprecation was more complicated than I expected.