Add tests and fix parameter exploding issue

[hamir-suspect]

This fixes the parameters exploding issue. Now parameters defined as:

parameter(
            :some,
            :query,
            %Schema{
              type: :object,
              oneOf: [
                %Schema{
                  type: :object,
                  properties: %{foo: %Schema{type: :string}, bar: %Schema{type: :string}},
                  required: [:foo]
                },
                %Schema{
                  type: :object,
                  properties: %{foo: %Schema{type: :string}, baz: %Schema{type: :string}},
                  required: [:baz]
                }
              ]
            },
            "Some query parameter ",
            explode: true,
            style: :form,
            required: true
          )

will be properly casted into the :some parameter.
How this works:
the parameters that we fetch for a location can be flat (?foo=x&bar=y) before casting we search for any parameters that should be exploded, if we find any we gather all the properties it can hold.
We add those to the struct (as if it was a deep struct param ?some[foo]=x&some[bar]=y and remove them from the query params. in the end query params struct before casting looks like %{"some" => %{"foo" => "x", "bar" => "y"}} instead of what we started with: %{"foo" => "x", "bar" => "y"}.

The ideal way would be to fix how the location schema is composed but that seems to be quite tricky with current implementation.

The PR has some leftover code from experimentation, if you think this is a good solution I will clean it up.

[hamir-suspect]

This PR resolves #573 , I would welcome any suggestions for improvements.

[mbuhot]

Thanks for the PR @hamir-suspect, I'm a bit concerned about the complexity required to identify all potential parameters that may apply to an exploded form style query parameter object.

Could we simplify the approach by taking all query params, then remove those with names matching non-exploded Parameters? All remaining query params are potentially consumed by exploded Parameters and will be passed along to Cast, leaving it up to the existing polymorphic schema handling to determine which ones are included in the result.

[hamir-suspect]

@mbuhot thanks for the feedback. I've cleaned up the PR a little bit and removed params with names matching to non-exploded schema parameters.