[BUG][PGFPlotsX][Unitful] setting axis labels duplicates units

[xwjqv]

When setting axis labels while using units and the PGFPlotsX backend,
the units appear twice in the label.

This probably happens because of the changes in #4723.
The units are also incorrectly italicized (maybe use UnitfulLatexify.jl for it)

Details

Example

using Plots, Unitful
pgfplotsx()
plot([1u"s",2u"s"],[1u"m",2u"m"],xlabel="t",ylabel="r")

crashing example

This has probably the same cause as #4722

using Plots, Unitful
pgfplotsx()
plot([1u"s",2u"s"],[1u"m/s^2",2u"m/s^2"],xlabel="t", ylabel="a")

Backends

This bug occurs on ( insert x below )

Backend	yes	no	untested
gr (default)		x
pythonplot			x
plotlyjs		x
pgfplotsx	x
unicodeplots		x
inspectdr		x
gaston		x

Versions

Plots.jl version: master
Backend version (]st -m <backend(s)>): PGFPlotsX v1.5.3
Output of versioninfo():

Julia Version 1.8.5
Commit 17cfb8e65ea (2023-01-08 06:45 UTC)
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 16 × AMD Ryzen 7 1700 Eight-Core Processor
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-13.0.1 (ORCJIT, znver1)
  Threads: 8 on 16 virtual cores
Environment:
  JULIA_REVISE_WORKER_ONLY = 1

[BeastyBlacksmith]

CC: @t-bltg

[t-bltg]

Hum sorry for this.

Unitful was written for GR and we never tested it on PGFPlotsX (neither in regression tests). So everything is left to be correctly implemented here.

There are choice to be made. I'd say that the units should be in math mode for handling braces/parens (hence rendered slightly italicized). But it's to be discussed.

Contributions welcome 🙂.

Ping @gustaphe for discussion.

[gustaphe]

UnitfulLatexify has a recipe for (label, unit) tuples, so plot(rand(5)u"m", rand(5)u"s"; unitformat=latexify, xguide="x", yguide="t") looks good in GR. I have not tried it in pgfplotsx but perhaps that's the solution here? One of these days I may find some time to look at it.

[gustaphe]

I can't find where, but somewhere the UnitString guide is transformed into a String when using pgfplotsx.

[gustaphe]

Nvm, found it in the fix to the linked issue.

The overloading of the guide attribute is a bit of a problem: UnitfulExt uses it to store information about the axis units. It's clever, but not necessarily in the good way.
Either pgfplotsx should change to storing the UnitfulString and transforming it at the printing point, or we should think of a less cludge way to keep track of axis units. I have no good suggestions.