fix(archive): reject unsupported formats

[pttydou]

Description

Fixes #97.

Validates format during YAML loading so unsupported values return a configuration error instead of calling a nil archive constructor. Adds a regression test for format: rar.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation and I have updated the documentation accordingly.
• I have added tests to cover my changes.

Test plan

• go test ./internal/pkg/pipeline/task/archive -count=1
• go test ./... -count=1 — the archive package passes, but the full command cannot compile the existing confluent-kafka-go dependency on Windows with CGO_ENABLED=0 (undefined: kafka.LibraryVersion). Linux CI covers the remaining build.