openapi: querystring parameters are stamped with a style the spec forbids

[OmarAlJarrah]

What happens

compilers/openapi/internal/operation/params.go:326 defaultParamStyle puts
soa.ParameterInQueryString in the same arm as query and cookie, so a 3.2
in: querystring parameter comes out of the compiler carrying
style: "form" and explode: true:

- name: querystringWhole
  in: querystring
  content:
    application/x-www-form-urlencoded:
      schema: {type: object}

{'param': 'querystringWhole', 'location': 'querystring', 'style': 'form',
 'explode': True, 'contentType': 'application/x-www-form-urlencoded'}

Why it is wrong

style is not a legal keyword on this location. OpenAPI 3.2 binds the whole
query string from the parameter's content, and forbids both style and
schema there — the bundled parser refuses the declaration outright
(openapi/parameter.go: "parameter field style is not allowed for
in=querystring"). So the IR records a declared serialization fact that the
source cannot state and that no reader can have meant, and an emitter reading
style: form would serialize the parameter as a form-exploded field rather than
as the media type contentType already names.

The function's own doc comment describes the table as "query/cookie →
form/true, path/header → simple/false" and does not mention querystring, so the
third location in that arm reads as an oversight rather than a decision.

Expected

A querystring binding carries no style and no explode — the media type in
ContentType is the whole of its declared serialization.

Where it is pinned today

testdata/conformance/openapi/param-style-matrix.yaml exercises the location and
assertQuerystringParam in compilers/openapi/conformance_test.go pins the
current values with a comment citing this issue, so fixing it reddens that case
and the golden rather than passing unnoticed.