Fix double decoding of URL query values

[winklemad]

Description of change

urllib.parse.parse_qs already percent-decodes query values. Both the sync and
async URL parsers subsequently called unquote on those values, causing
doubly encoded data such as %2520 to become a space instead of the literal
%20.

Remove the redundant second decoding step in both implementations and add
mirrored sync/async regression tests proving query values are decoded exactly
once.

Fixes #4208

Pull Request check-list

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  • Focused tests, all 83 URL-parsing tests, Ruff checks and formatting for
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Note

Low Risk
Small, localized URL parsing fix with mirrored tests; no auth or API surface changes beyond correct query string values.

Overview
Fixes double percent-decoding of connection URL query parameters in sync and async parse_url by dropping an extra unquote() on values returned from parse_qs, which already decodes them once.

Values like client_name=worker%2520name now become the literal worker%20name instead of worker name. Username, password, path, and host handling are unchanged and still use unquote where appropriate.

Adds matching sync/async pool tests (test_querystring_values_are_decoded_once) to lock in single-decode behavior (fixes #4208).

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[Sanjays2402]

this contradicts the from_url docstrings, which state "The username, password, hostname, path and all querystring values are passed through urllib.parse.unquote". Same text lives in client.py:185, cluster.py:660, asyncio/client.py:172 and asyncio/cluster.py:344, so all four need the querystring part dropped or this becomes an undocumented behavior change for anyone who double-encoded on purpose.