Drop Support for Julia 1.9

[svchb]

Following things need to be changed to drop Julia 1.9:

• DiffEqCallbacks >4 (see Fix callback show and remove hacky workaround #669)
• Remove finalize from 'SolutionSavingCallback' (see Fix callback show and remove hacky workaround #669)

[efaulhaber]

And this can be removed:

TrixiParticles.jl/test/validation/validation.jl

Lines 50 to 62 in e80d820

	if VERSION == v"1.10"
	@test isapprox(error_edac_P1, 0, atol=eps())
	@test isapprox(error_edac_P2, 0, atol=eps())
	@test isapprox(error_wcsph_P1, 0, atol=eps())
	@test isapprox(error_wcsph_P2, 0, atol=eps())
	else
	# 1.9 causes a large difference in the solution
	# TODO 1.11 requires a performance hotfix which will likely change these results again
	@test isapprox(error_edac_P1, 0, atol=4e-9)
	@test isapprox(error_edac_P2, 0, atol=3e-11)
	@test isapprox(error_wcsph_P1, 0, atol=26.3)
	@test isapprox(error_wcsph_P2, 0, atol=8.2e-3)
	end

[efaulhaber]

And the minimum version 1.9 is mentioned in the README and install.md.

[efaulhaber]

I guess PointNeighbors.jl tests on 1.9 will also fail when TrixiParticles requires Julia 1.10. TrixiParticles is used as a test dependency to run the benchmarks.

[sloede]

If you are dropping v1.9 support here, I'd definitely do it also for PN

[efaulhaber]

See trixi-framework/PointNeighbors.jl#93