Add samplesheetparser/diff module

[chaitanyakasaraneni]

What

Adds a new module samplesheetparser/diff that compares two Illumina SampleSheet.csv files (V1 or V2) and emits a structured JSON diff.

Why

This is the next module in the samplesheetparser family (after info and validate merged in #11604). The diff subcommand is useful as a CI pre-run guard: it surfaces header
changes, added/removed samples, and per-sample field changes between two sheets, and exits non-zero when differences are detected.

Changes

• New module modules/nf-core/samplesheetparser/diff/ with:
  • main.nf — wraps samplesheet diff, emits *.diff.json and versions
  • meta.yml — input/output schema with EDAM ontologies, tool metadata
  • environment.yml — bioconda samplesheet-parser=1.2.0
  • tests/main.nf.test + .snap — three tests (V1 vs V1 identical, V1 vs V2 cross-format, stub)
• Patterns applied proactively based on review feedback from Add samplesheetparser/info and samplesheetparser/validate modules #11604:
  • Container check supports both singularity and apptainer
  • No hardcoded CLI flags — callers pass options via ext.args
  • Stub uses touch for output files
  • Tests use sanitizeOutput(process.out) in snapshots
  • Versions emitted via topic: versions with versions_samplesheetparser emit name

PR checklist

Closes #XXX

• This comment contains a description of changes (with reason).
  • If you've fixed a bug or added code that should be tested, add tests!
  • If you've added a new tool - have you followed the module conventions in the contribution docs
  • If necessary, include test data in your PR.
  • Remove all TODO statements.
  • Broadcast software version numbers to topic: versions - See version_topics
  • Follow the naming conventions.
  • Follow the parameters requirements.
  • Follow the input/output options guidelines.
  • Add a resource label
  • Use BioConda and BioContainers if possible to fulfil software requirements.
  • Ensure that the test works with either Docker / Singularity. Conda CI tests can be quite flaky:
    • For modules:
      • nf-core modules test samplesheetparser/diff --profile docker
      • nf-core modules test samplesheetparser/diff --profile singularity
      • nf-core modules test samplesheetparser/diff --profile conda