Avoid computing derivative of constant nodes in matmul

[blegat]

On GPU

Before

BenchmarkTools.Trial: 10000 samples with 1 evaluation per sample.
 Range (min … max):  448.389 μs …  10.186 ms  ┊ GC (min … max): 0.00% … 0.00%
 Time  (median):     471.410 μs               ┊ GC (median):    0.00%
 Time  (mean ± σ):   485.842 μs ± 103.175 μs  ┊ GC (mean ± σ):  0.00% ± 0.00%

      ▁▆█▆▂                                                      
  ▁▁▂▄█████▇▅▄▃▃▃▃▂▂▂▃▄▅▇▆▅▄▃▂▂▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁ ▂
  448 μs           Histogram: frequency by time          607 μs <

 Memory estimate: 35.03 KiB, allocs estimate: 1139.

After

BenchmarkTools.Trial: 10000 samples with 1 evaluation per sample.
 Range (min … max):  366.680 μs …  7.760 ms  ┊ GC (min … max): 0.00% … 0.00%
 Time  (median):     389.702 μs              ┊ GC (median):    0.00%
 Time  (mean ± σ):   396.722 μs ± 79.007 μs  ┊ GC (mean ± σ):  0.00% ± 0.00%

            ▁▄▇█▆▅▃▁                                            
  ▁▁▂▂▂▂▃▄▅▆█████████▆▅▄▃▃▂▂▂▂▂▂▂▂▂▂▂▁▂▂▂▂▂▂▂▂▂▂▂▂▂▁▁▁▁▁▁▁▁▁▁▁ ▃
  367 μs          Histogram: frequency by time          459 μs <

 Memory estimate: 32.31 KiB, allocs estimate: 1045.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.23%. Comparing base (2275500) to head (2fea396).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #75      +/-   ##
==========================================
+ Coverage   90.61%   92.23%   +1.61%     
==========================================
  Files          24       25       +1     
  Lines        3017     3219     +202     
==========================================
+ Hits         2734     2969     +235     
+ Misses        283      250      -33     

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