fix: Instance of with correct duration names

[sccalabr]

Description

• instance of doesn't work for durations

Expected behavior

null instance of years and months duration -> false
null instance of days and time duration -> false

duration("P3M") instance of years and months duration -> true
duration("PT4H") instance of days and time duration -> true

Related issues

closes #155

[saig0]

@sccalabr thank you for your contribution. 🎉 I'll have a look at your PR in the next few days. 👀

[sccalabr]

Does this look good?

[saig0]

@sccalabr your changes look good. 🎉

I have a minor comment about the documentation. I'll adjust the docs myself and merge the PR. 🚀

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[saig0]

❌ The expression is wrapped into double quotes.

Suggested change

	"duration("P3M") instance of years and months duration"
	// true
	"duration("PT4H") instance of days and time duration"
	// true
	duration("P3M") instance of years and months duration
	// true
	duration("PT4H") instance of days and time duration
	// true

[saig0]

❌ We should update the type names in the description above.

We can replace the old names for the duration types. A user should use the official type names.