feat: add Karpenter, EKS, and Terraform output formats

[alexei-led]

Summary

Implements issue #15: Infrastructure-ready output formats for spotinfo.

Features

Three New Output Formats

1. Karpenter (--output karpenter)

Generates NodePool manifests with requirements for instance types, architecture, and capacity type.

2. eksctl (--output eksctl)

Generates eksctl managedNodeGroups YAML configuration snippets with Spot spot instance options.

3. Terraform (--output terraform)

Generates HCL locals block with spot_instance_types list for use in infrastructure-as-code.

Implementation

• Added printAdvicesKarpenter, printAdvicesEksctl, printAdvicesTerraform handlers in cmd/spotinfo/main.go
• Shared template helpers for instance type lists
• Updated output flag usage documentation
• Added unit tests for each format validating output structure
• All tests pass

Impact

This turns spotinfo from an exploration tool into a configuration tool — engineers can now copy-paste results directly into their Karpenter, EKS, and Terraform configs.

Fixes #15

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🤖 Automated response by Marvin • alexei-led