fix(filter): correct deep nested field validation in delete operations

[JosephDoUrden]

Summary

Fixes incorrect document deletion when using deep nested field filters
(e.g. main.items.{status: active && price: <100}).

---

Root Cause

validate_object_filter() in src/filter_result_iterator.cpp has two code paths:

• Batched path (when is_filter_result_initialized is true)
• Non-batched path (used during iterative AND/OR evaluation)

The batched path correctly used get_nested_field_doc() to traverse deep
nested JSON structures.

However, the non-batched path accessed:

document[filter_node->object_field_name]

This fails for multi-level paths such as main.items, because it attempts
to look up the literal key instead of navigating:

main → items

As a result, nested filters could match incorrectly, leading to unintended
document deletions.

---

Solution

Updated the non-batched path to use get_nested_field_doc(), making it
consistent with the batched implementation.

Before

for (const auto& nested_object: document[filter_node->object_field_name])

After

const auto& doc = get_nested_field_doc(filter_node->object_field_name, document);
for (const auto& nested_object: doc)

---

Files Changed

• src/filter_result_iterator.cpp
  → Use get_nested_field_doc() in non-batched validation path (1-line fix)

• test/core_api_utils_test.cpp
  → Added two test cases covering nested and deep-nested delete filters

---

Test Plan

Added:

• DeleteDocumentsWithNestedFieldFilter
• DeleteDocumentsWithDeepNestedFieldFilter

Both tests verify:

• Only matching documents are deleted
• Non-matching documents remain
• AND conditions within the same nested object are respected

Run tests:

bazel test //:typesense-test --test_filter="CoreAPIUtilsTest.DeleteDocumentsWithNestedFieldFilter"

bazel test //:typesense-test --test_filter="CoreAPIUtilsTest.DeleteDocumentsWithDeepNestedFieldFilter"

Or full suite:

bazel test //:typesense-test

---

Checklist

• Minimal fix (single logic change)
• Tests added
• No unrelated refactors

Closes #2765