[update] xeniumranger import segemtnation

[heylf]

Add expansion_distance parameter to xeniumranger/import-segmentation

What changed

• New optional expansion_distance input: the module now accepts an
  expansion_distance value (integer, microns) in the input tuple and passes it to
  xeniumranger as --expansion-distance=<value> when provided.
• Guarded by nuclei: the flag is only emitted when a nuclei segmentation file
  is also supplied. xeniumranger rejects --expansion-distance for
  transcript-assignment imports (proseg/baysor/segger) and cells-only imports, since
  expansion only makes sense when expanding nuclei into cell boundaries.
• Tests updated: both nf-test cases in tests/main.nf.test now pass 5 as the
  expansion_distance argument to match the new process input signature.
• Changing name from import-segementation to importsegmentation: To follow the rule: Module name should not have any punctuation.

Why

--expansion-distance controls how far nuclei are expanded outward to approximate
cell boundaries, so it only applies to nuclei-based imports. Passing it unconditionally
would break transcript-assignment and cells-only import runs, since xeniumranger
errors out when the flag is used without --nuclei. Making the flag conditional keeps
all three import modes working from a single process definition.

Testing

• Updated the two existing nf-test snapshot tests in
  modules/nf-core/xeniumranger/import-segmentation/tests/main.nf.test to supply the
  new expansion_distance value, keeping them in sync with the updated input tuple.

Files changed

• modules/nf-core/xeniumranger/import-segmentation/main.nf
• modules/nf-core/xeniumranger/import-segmentation/meta.yml
• modules/nf-core/xeniumranger/import-segmentation/tests/main.nf.test

PR checklist

Linked to issue: nf-core/spatialaxe issue #186

• This comment contains a description of changes (with reason).
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