Drop support for Julia 1.9

[efaulhaber]

Closes #688 and #672.

Depends on trixi-framework/PointNeighbors.jl#93.

[efaulhaber]

Needs trixi-framework/PointNeighbors.jl#95.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 69.88%. Comparing base (e80d820) to head (a9bf66e).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
test/count_allocations.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #703      +/-   ##
==========================================
- Coverage   69.89%   69.88%   -0.02%     
==========================================
  Files          87       87              
  Lines        5475     5476       +1     
==========================================
  Hits         3827     3827              
- Misses       1648     1649       +1     

Flag	Coverage Δ
unit	69.88% <75.00%> (-0.02%)	⬇️

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