Error handling for Objects that fail because they're too big

[snarfed]

Started seeing this error yesterday on https://maurice-renck.de/de/blog/2023/podcaster-plugin-3 (parsed mf2), which includes a big inlined data: img. Datastore raised google.api_core.exceptions.InvalidArgument: 400 entity is too big, which we don't yet handle, so we 500ed.

Datastore max property value size and entity size are both 1MB. OK. Total parsed mf2 size is only 200KB though, and the converted as1 computed property is similarly ~200KB. So why does the datastore think we're over 1MB?

...arguably it doesn't matter, we should just handle this exception and return HTTP 400.

[snarfed]

#1501 is probably the most common cause of this, doing that should help here.

[snarfed]

Did #1501, haven't seen this in the last 30d. Tentatively closing.