Add pair selecting support for cond-> and cond->> forms

[jramosg]

What has changed?

This PR adds support for growing selection to consider test/expr pairs in cond-> and cond->> threading forms, similar to how it works for cond and binding forms like let.

• Updated src/cursor-doc/paredit.ts to include cond-> and cond->> in conditional forms with correct offset handling.
• Added unit tests in src/extension-test/unit/cursor-doc/paredit-test.ts for pair selecting in threading forms.
• Updated CHANGELOG.md with an enhancement entry linking to issue Pair selecting in cond #2991.
• Added test data in test-data/test-files/paredit_sandbox.clj for the new forms.

Fixes #2991

My Calva PR Checklist

I have:

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  • Updated the [Unreleased] entry in CHANGELOG.md, linking the issue(s) that the PR is addressing.
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