fix(anota2seq): add gene IDs and handle empty results

[pinin4fjords]

This PR fixes several issues with the anota2seq module:

Problems Fixed

1. Missing gene IDs: The anota2seq results tables were missing gene identifiers, making it difficult to interpret results
2. Missing parameter: The parameter was used but never defined
3. Empty file handling: When no genes passed significance thresholds, the module would create empty/malformed files
4. Output expectations: Nextflow expected files that might not be created

Changes Made

• Add parameter: Defaults to "gene_id" but configurable
• Include gene IDs: Add gene identifiers as the first column in all results tables using and
• Conditional output: Only write files when there are actual results to avoid empty files
• Optional outputs: Mark all results TSV files as optional since they're now conditionally created
• Update tests: Modified test to use buffering results instead of empty mRNA_abundance, updated snapshots

Benefits

• Results tables now include gene identifiers for downstream analysis
• Consistent with other nf-core modules that include gene IDs
• Graceful handling of cases where no genes pass significance thresholds
• More robust error handling

Testing

• Updated test snapshots with new MD5 hashes reflecting the gene_id column addition
• Test now uses buffering results instead of empty mRNA_abundance results
• All outputs marked as optional to handle conditional file creation

The anota2seq results are now much more usable and consistent with expectations from other differential analysis modules.