Add repository URL generation feature

[zhisme]

Implement comprehensive repository URL generation when copying code snippets, transforming output to include direct permalinks to the code in GitHub, GitLab, or Bitbucket.

Features:

• Automatic git repository detection and remote URL parsing
• Support for GitHub, GitLab, and Bitbucket (including Enterprise/self-hosted)
• Always uses commit SHA for stable permalinks
• Lazy provider detection with extensible architecture
• Graceful degradation when not in a git repo
• Configurable via include_remote_url option (default: true)

Implementation:

• New git.lua module for git operations
• Provider architecture with lazy loading
• Integration into existing utils.format_output
• Comprehensive test coverage for all components
• Updated documentation with examples

Supported URL formats:

• GitHub: /blob/{sha}/{path}#L{start}[-L{end}]
• GitLab: /-/blob/{sha}/{path}#L{start}[-{end}]
• Bitbucket: /src/{sha}/{path}#lines-{start}[:{end}]

Handles edge cases:

• Detached HEAD, submodules, multiple remotes
• Windows path conversion, untracked files
• HTTPS, SSH, and git:// protocol URLs

fixes #1

[codecov]

Codecov Report

❌ Patch coverage is 99.58814% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
tests/copy_with_context/git_spec.lua	98.48%	4 Missing ⚠️
lua/copy_with_context/main.lua	96.77%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[zhisme]

Overview

This PR replaces the boolean include_remote_url flag with a flexible mapping and format system that allows users to define unlimited custom mappings with their own format strings.

Motivation

The previous implementation had a major usability issue: users could only toggle remote URLs on/off globally. This meant:

• ❌ No way to have separate keybindings for different output formats
• ❌ Users had to choose between file paths OR remote URLs, not both
• ❌ No flexibility to create custom format combinations

The new design allows users to:

• ✅ Define unlimited custom mappings (e.g., relative, absolute, remote, full, custom)
• ✅ Each mapping can have its own unique format string
• ✅ Mix and match variables: {filepath}, {line}, {linenumber}, {remote_url}
• ✅ Configuration validation prevents errors before runtime

Breaking Changes

Old Configuration:

require('copy_with_context').setup({
  mappings = {
    relative = '<leader>cy',
    absolute = '<leader>cY'
  },
  context_format = '# %s:%s',
  include_remote_url = true,
})