Support decoding of a struct nested into an array

[alexejk]

Fixes an issues where responses that have an outer array with a nested struct and other mixed types would not be decoded correctly, throwing a panic.

Example response:

<methodResponse>
  <params>
    <param>
      <value>
        <array>
          <data>
            <value>
              <i4>200</i4>
            </value>
            <value>OK</value>
            <value>
              <struct>
                <member>
                  <name>status</name>
                  <value>OK</value>
                </member>
                <member>
                  <name>contact</name>
                  <value>&lt;sip:raf@192.168.164.128:5060&gt;;expires=60</value>
                </member>
              </struct>
            </value>
          </data>
        </array>
      </value>
    </param>
  </params>
</methodResponse>

Correct way of mapping this response is to

struct{
    Array []any
}

Main issue with decoding this response prior to this PR, would be that any in array type is not assignable as is with decoded types.
This PR changes the logic to detect if an interface is mapped when attempting to decode a <struct> and assign a map[string]any to the field instead.

Fixes #84

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.91%. Comparing base (96e03e7) to head (1f615e0).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #85      +/-   ##
==========================================
+ Coverage   77.52%   77.91%   +0.39%     
==========================================
  Files           7        7              
  Lines         565      575      +10     
==========================================
+ Hits          438      448      +10     
  Misses         96       96              
  Partials       31       31              

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