Update docs and add descriptive error message

[efaulhaber]

• Removed the non-existent kwarg periodicity from the docstrings.
• Added a descriptive error message when the type of the periodic box does not match the type of the search radius and also added a note to the docs.

Find the rendered docs for this PR here:
https://trixi-framework.github.io/PointNeighbors.jl/previews/PR128/

[Copilot]

Pull Request Overview

This PR improves error handling and documentation for neighborhood search functionality by adding type checking between search radius and periodic box parameters, and cleaning up outdated documentation.

• Added type validation to ensure search_radius and PeriodicBox have matching element types
• Removed references to non-existent periodicity parameter from docstrings
• Added documentation note about type requirements for single precision usage

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/nhs_grid.jl	Added type validation and documentation note about type matching requirements
src/neighborhood_search.jl	Added eltype method for PeriodicBox to support type checking
src/cell_lists/full_grid.jl	Cleaned up docstring by removing non-existent periodicity parameter

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[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 87.84%. Comparing base (edf29bb) to head (022380d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/nhs_grid.jl	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #128      +/-   ##
==========================================
- Coverage   87.94%   87.84%   -0.11%     
==========================================
  Files          15       15              
  Lines         622      625       +3     
==========================================
+ Hits          547      549       +2     
- Misses         75       76       +1     

Flag	Coverage Δ
unit	87.84% <66.66%> (-0.11%)	⬇️

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