Handle pagination in cluster stack listing (#349)

[FarhanTejani]

What's changing and why?

Closes #349

HpClusterStack.list() calls cf.list_stacks() once and returns the result without pagination. In accounts with many CloudFormation stacks, the response is truncated and stacks are silently missing from the output.

This change adds a pagination loop that follows NextToken until all pages are collected.

Before/After UX

Before:

• hyp list hyp-cluster returns at most one page of stacks (up to 100). Additional stacks are silently dropped.

After:

• hyp list hyp-cluster returns all stacks across all pages.

How was this change tested?

• Unit tests pass

Are unit tests added?

• Updated 1 test that expected an empty dict for empty responses (now returns {'StackSummaries': []} for consistent shape)
• Added 1 test that exercises the pagination path (multi-page response with NextToken)

Are integration tests added?

N/A

Reviewer Guidelines

‼️ Merge Requirements: PRs with failing integration tests cannot be merged without justification.

One of the following must be true:

• All automated PR checks pass
• Failed tests include local run results/screenshots proving they work
• Changes are documentation-only