fix(waterdata): raise RequestTooLarge for an unchunkable over-budget request (not a silent 414)

[thodson-usgs]

Problem

ChunkPlan's "no chunkable axes" branch returned immediately without sizing the request — its comment even said "if that produces an over-budget URL, the server (or httpx itself) rejects." So a single large CQL-text filter with one big IN (...) clause — which has no top-level OR, hence yields no chunk axis — was shipped verbatim and failed with an opaque HTTP 414, not even a RequestTooLarge:

ids = ", ".join(f"'USGS-{i:08d}'" for i in range(1000))
get_daily(filter=f"monitoring_location_id IN ({ids})", filter_lang="cql-text")
# 17 KB request -> 414, no actionable error
# (the equivalent get_daily(monitoring_location_id=[...]) chunks fine)

Fix

Size-check the no-axes path: if the single request fits the byte limit, pass through exactly as before (the common hot path); if it's over budget there's nothing to split, so raise RequestTooLarge with actionable guidance (narrow the query / simplify the filter / split manually) instead of shipping it.

Verification

(a) 1000-id CQL IN filter -> RequestTooLarge ✓   (was: shipped -> 414)
(b) small scalar query    -> passthrough (0 axes), no raise ✓
(c) monitoring_location_id=[2000 ids] -> chunked (1 axis), no raise ✓

The chunking suite passes (the old test that asserted "pass an over-budget request through (the server may 414)" is updated to expect RequestTooLarge, plus a fits→passthrough case). ruff clean.

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