fix: remove gocsv dependency

[aaguiarz]

Remove the github.com/gocarina/gocsv dependency by implementing a local CSV marshaler using stdlib encoding/csv and reflect for struct tags.

Files:

• internal/output/marshal.go:77
• cmd/tuple/read.go:50–58

Changes:

• Create a local marshalCSV(data any) helper function using encoding/csv and reflect
• Parse csv struct tags to generate headers and rows
• Replace gocsv.MarshalBytes() call with the new helper