Calling limit()/offset()/range() twice sends duplicate query params

[twelfthlabor]

Calling .limit() twice on one chain sends both values:

client.from_("t").select("*").limit(10).limit(20)
# sends: select=*&limit=10&limit=20

Same for .offset() and .range(). On current main these use params.add() while order() uses params.set() and merges, so this looks like an oversight.

Concrete problem: against local PostgREST 16.2 the server applies the last value (20 wins), but params["limit"] on the built request returns the first (10). The client disagrees with the server about what the query is.

Note this differs from #1208, which is about reusing a builder across executes. This is setter semantics in a single chain. Foreign-table variants share the same .add path.