Decoder: Support for nested mixed-type arrays

[alexejk]

Updating decoder's logic for handling slices in order to support nested []any types decoding.

This in particular happens when response contains arrays of mixed types including multi-level nested mixed type arrays, such as:

<?xml version="1.0"?>
<methodResponse>
	<params>
		<param>
			<value><string>OK</string></value>
		</param>
		<param>
			<value><int>200</int></value>
		</param>
		<param>
			<value>
				<array>
					<data>
						<value><i4>200</i4></value>
						<value><array><data><value>Some String</value></data></array></value>
						<value>Server: Sip Express Media Server (5.1.0 (x86_64/Linux)) calls: 0 active/0 total/0 connect/0 min</value>
					</data>
				</array>
			</value>
		</param>
	</params>
</methodResponse>

This kind of response should be handled as

	type Response struct {
		Status string
		Code   int
		Data   []any
	}

However Data could not be processed due to Decoder previously expecting a Slice type (and primitive ones) when handling arrays. This however would cause an issue on the second element of the <array> which happens to be another <array>. With this PR decoder now can properly handle interface type when attempting to parse <array> and thus can handle nested arrays.

Fixes #86

[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 78.29%. Comparing base (c1e7cf1) to head (78203c0).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #87      +/-   ##
==========================================
+ Coverage   77.91%   78.29%   +0.37%     
==========================================
  Files           7        7              
  Lines         575      585      +10     
==========================================
+ Hits          448      458      +10     
  Misses         96       96              
  Partials       31       31              

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