TimedeltaBlock.fillna treats int as second

[jbrockmendel]

Seems like assuming nanosecond would be more natural, or just refusing to assume.

https://github.com/pandas-dev/pandas/blob/master/pandas/core/internals.py#L1981

[jbrockmendel]

There's only one test that hits this and its benign because it happens to fill with 0.

[jreback]

yeah this is probably not idea, does this show up in user facing code?

[jbrockmendel]

Closed by #24694