[ATR-22330] Force TDT to reload config on file boundary

For historic reasons, the Trigger Decision Tool maintains an internal configuration cache.

In r22 in AthenaMT, the in-file config is now distinct from the in-memory config to support MT. But in (serial) AnalysisBase the config is still served directly from the file.

It appears that the TDT's cache directly references objects within this in-file config data, and as such the cache must be refreshed on the file boundary when the pointers to the outgoing file become invalidated - even if the config hasn't actually changed.

While this isn't needed for MT, I added the same behaviour here too for consistency's sake. Here it will trigger once per processing slot, on the first event of the new file seen by each slot.