refactor: improve usage tips

[kricsleo]

resolves #147

This PR aims to enhance the usage tips, making them more readable and less confusing.

• Added (Default: ...) to descriptions when default: ... is set.
• Moved (required) from the argument part to the description.
• Added fallback value hints using snake_case names to avoid confusion when multiple args are displayed together (Improve arg help usage message (placeholder) #147).

Mainly referenced https://clig.dev/

Looking forward to your feedbacks! ❤️

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[codecov]

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Additional details and impacted files

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  Coverage        ?   94.03%           
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  Files           ?        7           
  Lines           ?      520           
  Branches        ?      163           
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  Hits            ?      489           
  Misses          ?       31           
  Partials        ?        0           

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