`nf` seems to have wrong prototypes

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p5.js version

main branch

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Steps to reproduce this

This is generally a report about the documentation and test cases.

From the reference, the prototypes for nf are:

• nf(num, [left], [right])
• nf(nums, [left], [right])

However, from the source code, especially in doNf(num, left, right), there isn't check of type left === 'undefined', nor a default value for left, so when calling leftPart = leftPart.padStart(left, '0'), left cannot be undefined.

Also in the test suite of p5.prototype.nf, test cases are missing:

• result = nf(1234), if left is optional
• result = nf([1234, 3.141516, 3.141516e-2], 2) for an array of numbers to format

Start at doNf(num, left, right) and the p5.prototype.nf test suite, then compare their behavior with the documented nf prototypes in the reference. Check the optional-left and array-formatting cases described in the issue. Done means the implementation, tests, and reference documentation agree on supported arguments and behavior.