Optimisation: Use heapify in MutableBinaryHeap

[rushabh-v]

Fixes: https://github.com/JuliaCollections/DataStructures.jl/issues/639

Note: I was a little confused by the issue-description, so not sure if the changes I made are at the correct place.

[oxinabox]

@AquaIndigo can you review?

[oxinabox]

CI fails so i suspect this is not correct

[rushabh-v]

Turned out I haven't updated nodemap after calling heapify. I am wondering if we can do that efficiently (without using extra space).

Or does the issue intend to use heapify at some other place @AquaIndigo? (That was the confusion that I mentioned here)

[Indigo2233]

Turned out I haven't updated nodemap after calling heapify. I am wondering if we can do that efficiently (without using extra space).

Or does the issue intend to use heapify at some other place @AquaIndigo? (That was the confusion that I mentioned here)

I think that heapify! could help.

[rushabh-v]

I ran the tests locally, it was all green.

[oxinabox]

Sorry for taking so long to review this. I lost track of it

It may also need rebasing to get out new CI setup to work