feat: add IPv6 address support in URL parsing (fixes #400)

[Riventh]

Summary

Adds support for IPv6 addresses in WinRM endpoint URLs, enabling pywinrm to work in IPv6-only and dual-stack environments.

Problem

The Session._build_url() method could not parse IPv6 addresses in bracket notation (RFC 3986 format). The existing regex pattern only matched
IPv4 addresses and hostnames, causing URLs like http://[2a05:d018:1961:ba00:ff5b:37ba:20c7:726a]:5985/wsman to fail parsing.

Solution

Implemented dual-pattern regex matching:

1. First attempts to match IPv6 addresses in bracket notation: [[0-9a-f:]+]
2. Falls back to the original IPv4/hostname pattern if IPv6 doesn't match
3. Maintains full backward compatibility with existing functionality

Changes

• Updated Session._build_url() to support IPv6 bracket notation per RFC 3986
• Added 8 comprehensive test cases covering various IPv6 URL formats
• All existing tests pass without modification

Test Coverage

• Basic IPv6: [2a05:d018:1961:ba00:ff5b:37ba:20c7:726a] → http://[2a05:d018:1961:ba00:ff5b:37ba:20c7:726a]:5985/wsman
• IPv6 with port: [::1]:8080 → http://[::1]:8080/wsman
• IPv6 with scheme: https://[fe80::1] → https://[fe80::1]:5985/wsman
• IPv6 localhost: [::1] → http://[::1]:5985/wsman
• IPv6 with SSL transport
• Full URLs with IPv6 addresses

Validation

• ✅ All 77 existing tests pass
• ✅ All 8 new IPv6 tests pass
• ✅ Type checking passes (mypy)
• ✅ Code formatting passes (black, isort)
• ✅ No breaking changes

Fixes #400