feat: add linearDelay for retryDelay option

[yutak23]

This ought to fix #276.

To allow the delayFactor to be changed, linearDelay is implemented to return the function required by the retryDelay option.

[yutak23]

@mindhells, thank you for your review.

[mindhells]

thank you @yutak23 !
Only one more thing: it is required to sign the commits to merge your PR 🙏

[yutak23]

thank you @yutak23 ! Only one more thing: it is required to sign the commits to merge your PR 🙏

@mindhells
Added signatures.
However, the force push caused other commits to be unsigned.
Should I combine them into one commit and sign it?

[mindhells]

thank you @yutak23 ! Only one more thing: it is required to sign the commits to merge your PR 🙏

@mindhells Added signatures. However, the force push caused other commits to be unsigned. Should I combine them into one commit and sign it?

That'd be the best, so I don't have to bypass branch protections to merge 🙇

[yutak23]

@mindhells ,
I apologize for the trouble i have caused you.
I have pushed the commits together in a rebase and signed it.

[mindhells]

thanks a lot @yutak23 , this has been released as v4.5.0