ci: update workflows to use self-hosted runners

[amaydixit11]

Description:

Migrate all GitHub Actions workflows to use Hiero self-hosted runners to align with organization-wide security requirements and existing repository patterns.

• Replace runs-on: ubuntu-latest with hl-heka-lin-md across all workflows
• Ensure consistency with other Hiero repositories (e.g., DID SDK JS, Identity Collaboration Hub)
• Maintain existing workflow behavior while updating execution environment

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Related issue(s):

Fixes #6

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Notes for reviewer:

• This change follows the same migration pattern already applied in other Hiero repositories
• No functional changes to workflow logic; only runner environment updated
• All jobs should behave identically, but now execute on self-hosted runners as required by org policy

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Checklist

• Documented (Code comments, README, etc.)
• Tested (workflows should trigger on PR/push as before)

[tajang97]

LGTM. To be merged after the Heira team sets out the needed runners