fix(waterdata): send the qualifier filter as a JSON array

[thodson-usgs]

TL;DR: The service parses qualifier as a JSON array, so it responded with HTTP 400 to every value the Water Data getters sent. The getters now send "ICE" as ["ICE"] and a list as one array; the service matches the whole list, in order, and the docstrings now state this. The maintainer should confirm the exact-match behavior and make four edits when rebasing after #425.

Merge order is in #426.

Changes

• _get_args (waterdata/utils.py) encodes qualifier as one compact JSON array, from a named parameter or from **queryables (get_peaks). A string that starts with [ is sent unchanged; an empty list is still dropped.
• qualifier docstrings on the five getters that name it: "ICE" matches ["ICE"], not ["ESTIMATED", "ICE"].

For the maintainer

• Behavior change: a list matches that exact list in order, not any of its values. The service responds with 400 to the CQL2 array operators (a_contains, a_overlaps, a_equals), and this PR does not filter on the client. Before this change the service responded with 400 to any list, so no working call changes meaning.
• Rebase edits after feat(waterdata): name every column the OGC collections return #425: (1) keep both sides of the NEWS.md and get_continuous docstring conflicts; (2) add the exact-match sentence to feat(waterdata): name every column the OGC collections return #425's get_peaks qualifier docstring; (3) drop qualifier from feat(waterdata): name every column the OGC collections return #425's _NEWLY_NAMED table, whose plain-value assertion no longer holds; (4) in NEWS.md, write get_peaks() instead of "through **queryables".
• Set the NEWS.md date (09/29/2026) to the merge date.

Verification

• Offline: 1182 passed, 13 deselected, branch coverage 98.94%; ruff, mypy --strict, lint-imports, xenon, complexipy pass.
• Live on v0, get_daily at USGS-05420500, winter 2022–23: qualifier="ESTIMATED" returns 4 rows, ["ESTIMATED", "ICE"] 11, ["ICE", "ESTIMATED"] 0; get_peaks(qualifier="DIFFDATUM") returns 1. On main all four respond with 400. The new live test passes. The 400 was found by the 2026-09-29 live differential test of main against the feat(waterdata): request v1 of the Water Data API, pinnable through api_version #422–feat(waterdata): name every column the OGC collections return #425 stack.
• Rehearsed rebase onto the stack with the four edits: 1218 passed, same live results on v1.

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