std: Make std.PriorityQueue and std.PriorityDequeue unmanaged containers

[saurabh-mish]

#23431 had been dormant for a while.

This PR revives #21433 and resolves #21432.

[rohlem]

Unrelated to these changes, but it seems theres'a typo in the doc comment:
PriorityDeque says Order.gt if the third argument should be min-popped second,
while Queue says Order.gt if the third argument should be min-popped first.
From my understanding PriorityQueue is consistent here, the error for Deque was made in 22e1d92, but not in corresponding 82e8930.

(The wording is a bit clunky imo, I'd personally just replace the last part with "otherwise", or drop it since it's logically implied - but up to you or maintainers to decide.)

[saurabh-mish]

Summary of changes

Priority Dequeue

std.PriorityDequeue has method signatures similar to std.Deque

• Moved methods removeMinOrNull into removeMin and removeMaxOrNull into removeMax; updated tests.

• Renamed methods add, removeMin and removeMax to push, popMin and popMax repectively.

• Added new method isEmpty which returns true if the priority dequeue is empty and false if not. It is being used in addUnchecked, peekMin, removeMin, and removeMax.

Priority Queue

std.PriorityQueue has method signatures similar to std.PriorityDequeue

• Moved method removeOrNull into remove and updated corresponding tests.

• Renamed methods add to push and remove to pop.

• Added new method isEmpty method which returns true if the priority queue is empty and false if not. It is being used in peek and pop methods.

Moved Priority Dequeue into Priority Deque

TODO (this part will be edited based on progress, feedback, and observation)

• Add / improve doc comments
  • PriorityQueue
  • PriorityDeque
• Consistent fields: PriorityQueue has items, cap, and context, whereas PriorityDeque has items, len, context
  • Was struggling with this to be honest. If this is indeed an issue, I think it is beyond the scope of this PR.
• .empty value
  • PriorityQueue
  • PriorityDeque

[linux-user36]

Since there's already deque.zig, should this maybe be renamed to PriorityDeque for consistency?

[saurabh-mish]

Since there's already deque.zig, should this maybe be renamed to PriorityDeque for consistency?

I think so too, pushing PriorityDeque related changes shortly

[imomaliev]

IMHO we should not move simple checks like self.len > 0 to a function. It would have been needed if the empty state was complex or required some additional checks. Because it is just a length check, by adding this helper function we are actually making code slower, but without substantial readability improvements.

http://ithare.com/wp-content/uploads/part101_infographics_v08.png

[rohlem]

Small functions can (and are expected to) be trivially inlined by the compiler's optimization pass.

[saurabh-mish]

Adding an isEmpty method was intentional because its commonly used in general purpose programming. After adding it, I thought of actually using it in existing methods.

[saurabh-mish]

This PR is ready for review (updated the summary of changes).