Update GitHub workflows: remove CompatHelper, add Julia dependabot

[Krastanov-agent]

⚠️ Important: This enables dependabot only for the top-level Julia package. If there are any other sub-packages in subfolders, they will not be tracked by dependabot and may need separate configuration.

CC @Krastanov

Summary

• Remove CompatHelper workflows (replaced by dependabot)
• Add/update dependabot.yml with Julia and GitHub Actions ecosystems
• Julia dependabot support is now stable and preferred over CompatHelper

Changes

• Deleted any CompatHelper workflow files from .github/workflows/
• Updated/created .github/dependabot.yml with Julia and GitHub Actions ecosystem configurations
• Set weekly update schedule for Julia dependencies and GitHub Actions

Test plan

• Verify no CompatHelper workflows remain in .github/workflows/
• Confirm dependabot.yml has proper Julia and GitHub Actions ecosystem configurations
• Check that dependabot starts working after merge (may take up to 24 hours)

🤖 Generated with Claude Code

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Script source: https://gist.github.com/Krastanov-agent/2b049684a01788458c399e9441bb264a

[Krastanov]

leaving open as this repo is not in use right now (the package is in the lib folder of QuantumClifford.jl)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (d00dfa5) to head (60f1dee).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@    Coverage Diff    @@
##   main   #5   +/-   ##
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