Add path traversal validation in error.py following notion-sdk-js

[tsinglinrain]

Summary

• Add InvalidPathParameterError class for path traversal validation errors
• Add validate_request_path() function to detect path traversal sequences
• Add ClientErrorCode.InvalidPathParameter enum value
• Add comprehensive tests with 100% coverage on errors.py

This PR follows the JavaScript SDK's PR #661 to add path traversal prevention.
Related Issue #283

Differences from JS SDK

The Python implementation has two intentional differences from the JS version:

1. Simplified URL-encoded detection

# JS version
if (/%2e/i.test(path)) { ... }

# Python version
if "%2e" in path.lower():

Using in with str.lower() is more Pythonic than using regex for simple substring matching. So that we do not need to import re and it is more straightforward and easier to read. The reason for using a regular expression in JavaScript is that String.prototype.includes() does not support a case-insensitive option.

2. Removed try-except block

// JS version - needs try-catch because decodeURIComponent throws on invalid encoding
  try {
    decoded = decodeURIComponent(path)
  } catch {
    return
  }

# Python version - unquote() never throws, it preserves invalid sequences
decoded = unquote(path)

Python's urllib.parse.unquote() handles invalid percent-encoding gracefully by preserving the original characters, unlike JavaScript's decodeURIComponent() which throws URIError. The try-except block is unnecessary in Python. Furthermore, it makes it difficult to achieve 100% coverage.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b9d448d) to head (ed34105).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #312   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         7           
  Lines          480       496   +16     
=========================================
+ Hits           480       496   +16     

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[ramnes]

Great, thanks!