Clabverter Inline Startup Config Support

[bayars]

Summary

• Fix clabverter failing when startup-config contains inline content (YAML multiline "|") instead of a file path
• Add isInlineConfig() detection by checking for newlines in config value
• Re-serialize clabConfig when inline configs exist to update paths in topology definition

Changes

When a containerlab topology uses inline startup-config like:

startup-config: |
  /configure system name "router1"

clabverter was failing due to unexpected line error.

Test fixtures:

• Added test case with inline startup-config for both nokia_srlinux and nokia_srsim nodes
• Verified all 8 SR-SIM labs from containerlab repo convert successfully
• Existing tests continue to pass

[carlmontanari]

LGTM!