Make line numbers the default behavior for gpt-copy

[Copilot]

This PR makes line numbers enabled by default for gpt-copy, as requested in the issue. Line numbers are useful for referencing specific parts of files when working with LLMs, so they should be on by default.

Changes Made

Core Functionality

• Line numbers are now enabled by default - no flag required
• Added --no-number flag to disable line numbers when needed
• Kept -n/--number flag for backward compatibility
• --no-number takes precedence over -n if both are specified

Before vs After

Before (line numbers off by default):

gpt-copy /path/to/directory           # No line numbers
gpt-copy /path/to/directory -n        # Line numbers enabled

After (line numbers on by default):

gpt-copy /path/to/directory           # Line numbers enabled by default
gpt-copy /path/to/directory -n        # Line numbers enabled (redundant but supported)
gpt-copy /path/to/directory --no-number  # Line numbers disabled

Documentation Updates

• Updated README.md to reflect new default behavior
• Updated help text to show line numbers are enabled by default
• Updated "How It Works" section and feature list

Testing

• Added comprehensive tests for the new default behavior
• All existing tests continue to pass (24/24 tests passing)
• Backward compatibility maintained

Example Output

With line numbers now enabled by default:

## File: `example.py`
*(Relative Path: `example.py`)*

```python
1: def hello():
2:     print("Hello, World!")
3:     return True

Fixes #20.

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[simone-viozzi]

Remove the -n altogether

[Copilot]

Removed the -n flag completely as requested. Line numbers are now enabled by default with only --no-number to disable them when needed. This simplifies the interface since the -n flag was redundant. (ae95b81)

[simone-viozzi]

this is not present anymore

[Copilot]

Removed the redundant -n flag documentation section. (f59c4fb)

[simone-viozzi]

since line numbers are enabled by default, word it differently,
do an example to disable the line numers, and do not mention how to enable them, since they are already enabled

[Copilot]

Updated the documentation to focus only on disabling line numbers since they're now enabled by default. Removed the section about enabling them explicitly. (f59c4fb)

[simone-viozzi]

move it to line 544 and remove comment

[Copilot]

Moved the line numbers logic inline and removed the comment as requested. (f59c4fb)

[simone-viozzi]

LGTM you can merge the PR