feat: report size

[MatteoGabriele]

Description

This PR adds a size reporting feature that calculates and displays the sizes of bundled files in the output directory.

The implementation:

• Identifies and lists type declaration files (.d.ts, .d.mts, .d.cts)
• Calculates the raw, gzipped, and brotli size of each bundle file
• Computes and displays the total size across all bundle files
• Uses human-readable formatting for file sizes

Linked Issues

fix #116

Additional context

You might want to consider a different style and format for the logs, and it could be better to make this an optional feature instead of the default.

I hope I was able to help a little. Feel free to use the code as you see fit, or not at all.

Thank you for your work!

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commit: c3d6331

[sxzz]

Refactored a lot, thanks!