Add comprehensive test coverage and tooling improvements

[omsaisudarshan108]

Title: Add comprehensive test coverage and tooling improvements

Body:

Added extensive test cases for string_utils and url_utils modules
Added py.typed marker for PEP 561 compliance
Added codecov.yml for coverage tracking
Target branch: devel

Summary by CodeRabbit

• Tests

  • Expanded test coverage for string utility functions, including model conversion and string truncation scenarios.
  • Reorganized test structure for URL utility functions into a cohesive test suite.

• Chores

  • Added Codecov configuration for code coverage reporting.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

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[coderabbitai]

Walkthrough

This PR adds a Codecov configuration file with coverage reporting settings and branch detection rules, extends utility test coverage for string conversion and truncation operations, and reorganizes existing URL join tests into a cohesive test class.

Changes

Cohort / File(s)	Summary
Codecov Configuration codecov.yml	New configuration file defining coverage defaults (precision 2, range 70–100), status targets for project and patch, gcov branch detection settings, comment layout (reach, diff, flags, files), and ignore patterns for tests, examples, docs, and Python cache
String Utility Tests tests/nat/utils/test_string_utils.py	Adds comprehensive test suite for convert_to_str covering Pydantic BaseModel conversion, exclusion of None values, empty/nested collections, and primitive types; introduces new TestTruncateString class with tests for truncate_string edge cases (None, empty, exact length, ellipsis, custom length, type preservation)
URL Utility Tests tests/nat/utils/test_url_utils.py	Refactors 13 existing url_join test functions into instance methods within new TestUrlJoin class; no behavioral changes to test logic

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main changes: extensive tests for string_utils and url_utils, plus codecov.yml and py.typed additions for tooling improvements.
Docstring Coverage	✅ Passed	Docstring coverage is 93.10% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@codecov.yml`:
- Around line 51-56: The file ends without a trailing newline; update the YAML
by adding a single newline character after the last line of the ignore block
(the entry "**/conftest.py") so the file terminates with exactly one trailing
newline following the "ignore:" list.

🧹 Nitpick comments (4)

tests/nat/utils/test_string_utils.py (2)

16-22: Unused pytest import.

The pytest import on line 18 is not used in this file. The tests don't use pytest.raises, pytest.mark, or other pytest-specific features.

Proposed fix

 import dataclasses
 
-import pytest
 from pydantic import BaseModel
 
 from nat.utils.string_utils import convert_to_str
 from nat.utils.string_utils import truncate_string

---

89-134: Comprehensive truncate_string test class.

The test suite covers key scenarios well. Consider adding an edge case test for max_length < 3 to verify behavior when the ellipsis length exceeds available space.

Looking at the implementation (text[:max_length - 3] + "..."), when max_length=2, this would produce text[-1:] + "..." which may yield unexpected results.

Optional: Add edge case test

def test_truncate_max_length_less_than_ellipsis(self):
    """Test behavior when max_length is smaller than ellipsis length."""
    text = "Hello"
    result = truncate_string(text, max_length=2)
    # Document expected behavior for this edge case
    assert result is not None

tests/nat/utils/test_url_utils.py (2)

16-17: Unused pytest import.

The pytest import is not used in this file.

Proposed fix

-import pytest
-
 from nat.utils.url_utils import url_join

---

84-87: Weak assertion in test_url_join_preserves_protocol_slashes.

The assertion assert "http:" in result is very weak—it would pass for any URL containing "http:" anywhere. Consider a more specific assertion.

Proposed fix

     def test_url_join_preserves_protocol_slashes(self):
         """Test that protocol slashes are properly handled."""
         result = url_join("http://example.com", "path")
-        assert "http:" in result
+        assert result == "http://example.com/path"

[coderabbitai]

⚠️ Potential issue | 🟡 Minor

Missing trailing newline.

Per coding guidelines, every YAML file must end with a single newline. Add a newline after the last line.

Proposed fix

 ignore:
   - "tests/**/*"
   - "examples/**/*"
   - "docs/**/*"
   - "**/__pycache__/**"
   - "**/conftest.py"
+

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

	ignore:
	- "tests/**/*"
	- "examples/**/*"
	- "docs/**/*"
	- "**/__pycache__/**"
	- "**/conftest.py"
	ignore:
	- "tests/**/*"
	- "examples/**/*"
	- "docs/**/*"
	- "**/__pycache__/**"
	- "**/conftest.py"

🤖 Prompt for AI Agents

In `@codecov.yml` around lines 51 - 56, The file ends without a trailing newline;
update the YAML by adding a single newline character after the last line of the
ignore block (the entry "**/conftest.py") so the file terminates with exactly
one trailing newline following the "ignore:" list.

[willkill07]

/ok to test 208f93c