fix(apiquery): reject complex elements in comma arrays

[sylvesterkaczmarek]

Summary

Reject complex/keyed elements in comma-form query arrays instead of silently discarding their keys and flattening only their values.

Problem

internal/apiquery.encodeArray currently handles ArrayQueryFormatComma by recursively encoding each array element and appending every returned pair's value to the comma-delimited list. For map/object elements, that means the nested query keys are lost.

For example, a value shaped like:

map[string]any{
    "filter": []map[string]string{{"name": "alice"}},
}

can be reduced to a query equivalent to filter=alice, which no longer represents the original object structure and gives the caller no indication that serialization changed its meaning.

Fix

Require each comma-form element to encode to exactly one unkeyed scalar pair. If recursive encoding produces keyed or multiple pairs, return a clear apiquery error instead of emitting a corrupted query parameter.

Primitive comma arrays keep their existing behavior.

Regression coverage

Added focused tests proving that:

• an array containing map/object elements returns an error and no query values;
• an ordinary []string still encodes as alice,bob.

Validation

The branch is based directly on current upstream main (ee92673a416c0851a5fe8907a2453db7bd450633) and contains one commit touching only internal/apiquery/encoder.go plus focused regression coverage. Full Go test execution is left to repository CI.

Risk

Low. The newly rejected inputs are shapes whose key structure cannot be represented by the comma-array encoding. Existing primitive comma arrays and the repeat/indices/brackets array formats are unchanged.