feat(date): accept date as datetime.date not just str

[Danipulok]

What this PR does?

• Allow passing datetime.date as date;

What this PR does in details?

• Add _format_date method that formats both str and datetime.date;
• Update examples to use datetime.date;
• Checked both old formats and datetime.date work;

[upbit]

Great solution! Make compatible with various input types on the same parameter.

[upbit]

The code style - related adjustments have been merged. Please resolve the conflicting files and submit again.