test(stf): add unit tests for isValidIndexedAttestationIndices

Cover edge cases for the indexed attestation validation logic:
- Valid sorted unique indices
- Empty indices (reject)
- Single index (accept)
- Duplicate indices (reject)
- Unsorted indices (reject)
- Out-of-bounds index (reject)
- Boundary index (validators_count - 1 valid, validators_count invalid)
- Electra vs phase0 max indices limit

🤖 Generated with AI assistance

Author: lodekeeper-z

src/state_transition/block/is_valid_indexed_attestation.zig

@@ -72,3 +72,64 @@ pub fn isValidIndexedAttestationIndices(
 
     return true;
 }
+
+test "isValidIndexedAttestationIndices - valid sorted unique indices" {
+    const indices = [_]ValidatorIndex{ 0, 1, 5, 10, 100 };
+    const result = try isValidIndexedAttestationIndices(.phase0, 200, &indices);
+    try std.testing.expect(result);
+}
+
+test "isValidIndexedAttestationIndices - empty indices returns false" {
+    const indices = [_]ValidatorIndex{};
+    const result = try isValidIndexedAttestationIndices(.phase0, 200, &indices);
+    try std.testing.expect(!result);
+}
+
+test "isValidIndexedAttestationIndices - single index valid" {
+    const indices = [_]ValidatorIndex{42};
+    const result = try isValidIndexedAttestationIndices(.phase0, 100, &indices);
+    try std.testing.expect(result);
+}
+
+test "isValidIndexedAttestationIndices - duplicate indices returns false" {
+    const indices = [_]ValidatorIndex{ 1, 1 };
+    const result = try isValidIndexedAttestationIndices(.phase0, 200, &indices);
+    try std.testing.expect(!result);
+}
+
+test "isValidIndexedAttestationIndices - unsorted indices returns false" {
+    const indices = [_]ValidatorIndex{ 5, 3, 10 };
+    const result = try isValidIndexedAttestationIndices(.phase0, 200, &indices);
+    try std.testing.expect(!result);
+}
+
+test "isValidIndexedAttestationIndices - index out of bounds returns false" {
+    const indices = [_]ValidatorIndex{ 0, 1, 200 };
+    const result = try isValidIndexedAttestationIndices(.phase0, 200, &indices);
+    try std.testing.expect(!result);
+}
+
+test "isValidIndexedAttestationIndices - index at boundary valid" {
+    const indices = [_]ValidatorIndex{199};
+    const result = try isValidIndexedAttestationIndices(.phase0, 200, &indices);
+    try std.testing.expect(result);
+}
+
+test "isValidIndexedAttestationIndices - index at validators_count returns false" {
+    const indices = [_]ValidatorIndex{200};
+    const result = try isValidIndexedAttestationIndices(.phase0, 200, &indices);
+    try std.testing.expect(!result);
+}
+
+test "isValidIndexedAttestationIndices - electra allows more indices" {
+    // Phase0 max = MAX_VALIDATORS_PER_COMMITTEE (2048)
+    // Electra max = MAX_VALIDATORS_PER_COMMITTEE * MAX_COMMITTEES_PER_SLOT
+    var indices: [2049]ValidatorIndex = undefined;
+    for (&indices, 0..) |*v, i| v.* = @intCast(i);
+
+    const result_phase0 = try isValidIndexedAttestationIndices(.phase0, 10000, &indices);
+    try std.testing.expect(!result_phase0);
+
+    const result_electra = try isValidIndexedAttestationIndices(.electra, 10000, &indices);
+    try std.testing.expect(result_electra);
+}