Implement OAI 3.0 parameter style/explode serialization

[noha]

style/explode were parsed and stored on OAParameter but never applied when building a request - every parameter location silently ignored them and just called value asString, which also meant:

• Path parameters with a non-string value (e.g. a bare Integer id) crashed outright (ZnUrl>>addPathSegments: requires Strings).
• Header/cookie array values serialized as Smalltalk's Array printString (e.g. "#(3 4 5)") instead of a comma-joined string.
• matrix/label path styles, spaceDelimited/pipeDelimited/deepObject query styles, and explode:false were all silently no-ops.

Added a shared value-serialization layer on OAParameterLocation (isArrayValue:/isObjectValue:/explodeFor:/serializePairsFor:name: defaultStyle: and friends) implementing the full style matrix:

• path: simple (default), label, matrix
• query: form (default), spaceDelimited, pipeDelimited, deepObject
• header: simple only; cookie: form only
• explode defaults to true only for style:form, false otherwise; deepObject is only ever meaningfully defined with explode:true

Most styles produce a single serialized string; form+explode:true objects and deepObject flatten into multiple top-level query parameters instead (one pair per property), which is why serializePairsFor: returns a collection of key->value pairs rather than a single value - the query location adds each pair, while path/ header (which can never produce more than one) just take the first.

Cookies are a documented special case: the spec leaves form+ explode:true with a non-primitive value undefined for cookies (you can't repeat a cookie name the way you can repeat a query key), so arrays/objects are comma-joined into the single cookie value instead of expanded into separate pairs.

14 new tests covering the well-defined style/explode combinations, plus the two crash regressions (integer path parameter, array header/ cookie values). 27/27 OpenAPI-Client-Tests, 56/56 OpenAPI-Core-Tests, 4/4 OpenAPI-REST-Tests, 0 regressions.