Fix distribution bottleneck for higher dimensional grids

[BrianMichell]

In the trace_worker there was a hidden pickling bottleneck of the grid. This became very apparent on large ReceiverGathers3D datasets with a grid of ~200k chunks to process in this phase. The overall progress would only be able to use a single core due to GIL blocking.

This approach was selected to pay an nproc penalty to pickle to each process in the pool once, after which the resource should be recycled until the pool is drained.

[codecov]

Codecov Report

❌ Patch coverage is 40.00000% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.86%. Comparing base (c3ba558) to head (3c4dcd7).
⚠️ Report is 242 commits behind head on main.

Files with missing lines	Patch %	Lines
src/mdio/segy/_workers.py	29.41%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #832      +/-   ##
==========================================
+ Coverage   85.30%   92.86%   +7.55%     
==========================================
  Files          46      143      +97     
  Lines        2219     8168    +5949     
  Branches      306      462     +156     
==========================================
+ Hits         1893     7585    +5692     
- Misses        281      509     +228     
- Partials       45       74      +29     

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