Draft: Get rid of deprecation warnings

[nordlow]

Gets rid of deprecation warnings via:

1. body => do
2. rename variable to avoid shadow warning
3. approxEqual => isClose: I started updating all those darn floating point literals to a better precision to fit isClose's requirements but I got fed up with it because it wasted a lot of time and I couldn't find a way to automated it. So I added an approxEqual that mimics old deprecated version to make tests pass without warnings nor unittest failures. But kept the constants refactorings. I can continue updating the rest of literals if needed but I'd rather not. :)
4. git ignore dstats-test-library

Ready for review now, @John-Colvin .

For reference see https://dlang.org/changelog/2.096.0.html#deprecate-approxEqual.

[nordlow]

Shall I move

static if (__VERSION__ < 2096)
        alias approxEqual = std.math.approxEqual;
    else
        bool approxEqual(T, U, V)(T lhs, U rhs, V maxRelDiff = 1e-2, V maxAbsDiff = 1e-5)
        {
            return std.math.isClose(lhs, rhs, maxRelDiff, maxAbsDiff); // mimic old sloppy approxEqual for now
        }

to a common place? Say, base.d?

[skoppe]

What I understand from this:

• approxEqual is deprecated.
• isClose has higher precision demands.
• Because of that you had to up the precision of tested values.
• But there were too many so you didn't manage all.

It seems to me for the modules you did manage to fix you would want to use the isClose with the sane defaults.

Instead of hijacking approxEqual to call isClose on newer compiler, perhaps it is better to have isClose call approxEqual on older ones.

For the modules you didn't manage to fix you should not hide the deprecation warnings, however horrid they are.

[nordlow]

I think I've found a way to automate the precision refactoring of the assert constants...

[John-Colvin]

Shall I move

static if (__VERSION__ < 2096)
        alias approxEqual = std.math.approxEqual;
    else
        bool approxEqual(T, U, V)(T lhs, U rhs, V maxRelDiff = 1e-2, V maxAbsDiff = 1e-5)
        {
            return std.math.isClose(lhs, rhs, maxRelDiff, maxAbsDiff); // mimic old sloppy approxEqual for now
        }

to a common place? Say, base.d?

yes

[nordlow]

Gonna try update the constants now and hopefully get rid of the approxEqual wrapper altogether.