Add deprecation warning for Bazaar (bzr) support

[Copilot]

Bazaar is officially end-of-life and unmaintained. Users need to be warned when using bzr repositories.

Changes

• Deprecation warning in NewBzrRepo(): Logs warning via existing Logger mechanism before any operations
• Test coverage: TestBzrDeprecationWarning verifies the warning is logged correctly

Example

vcs.Logger = log.New(os.Stdout, "[VCS] ", log.LstdFlags)
repo, err := vcs.NewBzrRepo("https://launchpad.net/project", "/tmp/repo")
// Output: [VCS] WARNING: Bazaar (bzr) is deprecated and no longer maintained. 
//         Support for bzr may be removed in a future version.

The warning appears regardless of whether bzr is installed, ensuring all users attempting to use bzr are notified of its deprecated status.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Deprecate bzr</issue_title>
<issue_description>bzr has not been developed in years and is officially end of life. Without removing bzr support, it needs to be marked as deprecated with a warning being logged when it's used.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Deprecate bzr #118

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.