Add obisuperkmer command implementation and tests

This commit adds the implementation of the obisuperkmer command, including:

- The main command in cmd/obitools/obisuperkmer/
- The package implementation in pkg/obitools/obisuperkmer/
- Automated tests in obitests/obitools/obisuperkmer/
- Documentation for the implementation and tests

The obisuperkmer command extracts super k-mers from DNA sequences, following the standard OBITools architecture. It includes proper CLI option handling, validation of parameters, and integration with the OBITools pipeline system.

Tests cover basic functionality, parameter validation, output format, metadata preservation, and file I/O operations.

cmd/obitools/obisuperkmer/main.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"os"
+
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obioptions"
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obitools/obiconvert"
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obitools/obisuperkmer"
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiutils"
+)
+
+func main() {
+	// Generate option parser
+	optionParser := obioptions.GenerateOptionParser(
+		"obisuperkmer",
+		"extract super k-mers from sequence files",
+		obisuperkmer.OptionSet)
+
+	// Parse command-line arguments
+	_, args := optionParser(os.Args)
+
+	// Read input sequences
+	sequences, err := obiconvert.CLIReadBioSequences(args...)
+	obiconvert.OpenSequenceDataErrorMessage(args, err)
+
+	// Extract super k-mers
+	superkmers := obisuperkmer.CLIExtractSuperKmers(sequences)
+
+	// Write output sequences
+	obiconvert.CLIWriteBioSequences(superkmers, true)
+
+	// Wait for pipeline completion
+	obiutils.WaitForLastPipe()
+}