Type 'List<String>' is not a subtype of type 'String' in AlgoliaMultiIndexesReference

[SebastianWaloszek]

Dart version: 2.18.6
Flutter version: 3.3.10 (stable)

Describe the bug
When one sets a list of facet filters for a query to be performed as part of getObjects() inside AlgoliaMultiIndexesReference there's an encoding error being thrown.

dart:core                                        new _Uri
package:algolia/src/index_reference.dart 358:23  AlgoliaMultiIndexesReference._encodeMap
package:algolia/src/index_reference.dart 391:19  AlgoliaMultiIndexesReference.getObjects
test/algolia_test.dart 158:43                    main.<fn>.<fn>

type 'List<String>' is not a subtype of type 'String'

It only happens for AlgoliaMultiIndexesReference. When we try doing the same for AlgoliaIndexReference it works without issues.

To Reproduce
One can reproduce the issue in tests by adding a list of facet filters:

      queryA = queryA.facetFilter([
        'email:johan.1@example.com',
        'email:johan.2@example.com',
      ]);

in the Perform Multiple Queries test like this:

    test('Perform Multiple Queries', () async {
      var queryA = algolia.instance.index('contacts').query('john');
      var queryB = algolia.instance.index('contacts_alt').query('jo');

      // Perform multiple facetFilters
      queryA = queryA.facetFilter('status:published');
      queryA = queryA.facetFilter('isDelete:false');
      queryA = queryA.facetFilter([
        'email:johan.1@example.com',
        'email:johan.2@example.com',
      ]);

      try {
        // Get Result/Objects
        var snap = await algolia.multipleQueries
            .addQueries([queryA, queryB]).getObjects();
        // Checking if has [List<AlgoliaQuerySnapshot>]
        expect(snap.length, 2);
        print('Queries count: ${snap.length}');
      } on AlgoliaError catch (err) {
        print(err.error.toString());
        expect(err.runtimeType, AlgoliaError);
      }
      print('\n\n');
    });

Expected behavior
Encoding error should not happen inside AlgoliaMultiIndexesReference when the set facet filter for a query is a List<String>.

[SebastianWaloszek]

I have proposed a solution to this issue in this PR: #116