Various ticks fixes (precision, log scale)

[t-bltg]

1. Fix precision issues (fix optimize_ticks not working right for small values #114);
2. Relax exponent integer constraint when computing log based ticks (fix Spurious "no strict ticks" warning for log10 scales #116, fix [BUG] Log scale plots raise warning and break subsequent non-log scale plots Plots.jl#3918).
3. Coding style.
4. Update CI script, using julia LTS 1.6 and latest 1.7 (following test on 1.6 also Plots.jl#3966).
5. Drop julia versions < 1.6 for consistency with Plots.
6. Bump minor version.
7. Add formatting github action, as in Plots.

Xref: JuliaPlots/Plots.jl#3790, JuliaPlots/Plots.jl#3577, JuliaPlots/Plots.jl#3921.

Ran Plots.jl test suite without any apparent issue.

[t-bltg]

@BeastyBlacksmith, can you disable the AppVeyor CI action ? I don't think we'll use it anymore, and I don't have access to the settings of any JuliaPlots organization repo.

[BeastyBlacksmith]

In general I feel like this algorithm could try harder to show more than two ticks on log scales, but overall this is already an imrpovement

[ffreyer]

Looks like this messed up Makie's ticks in some cases.

With v1.0.15:

ticks = PlotUtils.optimize_ticks(0.25314125f0, 0.94421935f0, k_min = 4, k_max = 8)[1]
# [0.30000000000000004, 0.4, 0.5, 0.6000000000000001, 0.7000000000000001, 0.8, 0.9]
Showoff.showoff(ticks, :plain)
# ["0.3", "0.4", "0.5", "0.6", "0.7", "0.8", "0.9"]

With v1.1.0:

ticks = PlotUtils.optimize_ticks(0.25314125f0, 0.94421935f0, k_min = 4, k_max = 8)[1]
# Float32[0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.90000004]
Showoff.showoff(ticks, :plain)
# ["0.30000001", "0.40000001", "0.50000000", "0.60000002", "0.69999999", "0.80000001", "0.90000004"]

[t-bltg]

Ha, thanks for reporting, not surprising, will fix.

EDIT: Actually @ffreyer I'd expect optimize_ticks to return ticks with the same type as what was given as input for floats, why would it be otherwise ?

[ffreyer]

I'd expect that too. Maybe this should be fixed in Showoff or Makie?

[t-bltg]

I'd expect that too. Maybe this should be fixed in Showoff or Makie?

I'm not familiar with Showoff (I see lots of hardcoded Float64 in their algorithms), but the easiest would be to cast to Float64 in Makie:

$ grep -r optimize_ticks
src/basic_recipes/axis.jl:    scaled_ticks, mini, maxi = optimize_ticks(
src/basic_recipes/axis.jl:    scaled_ticks, mini, maxi = optimize_ticks(
src/makielayout/ticklocators/wilkinson.jl:    tickvalues, _ = PlotUtils.optimize_ticks(vmin, vmax;

, only 3 occurrences in Makie.

[t-bltg]

Seems like I introduced type instability in this PR, fix is underway ...