`get_pending_admin_state`: full pending state for admin dashboards

[usmanimamu17-create]

Problem Statement. get_pending_admin returns just the address.
Useful to know: time since proposal? Proposed-by-address?

Expected Outcome. New struct AdminProposalState { address, proposed_at_ledger, proposed_by }.
New fn: get_pending_admin_state. Same for operator.

Files: lib.rs, new tests.

[danfulani0]

Hi! I'm an enthusiastic developer who is eager to contribute to open source. I've reviewed the issue and I'm confident I can work through it carefully. I'll communicate my progress, write clean code, test my solution, and submit a pull request promptly. I'd appreciate the opportunity to contribute. Thank you!

[grantfox-oss]

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Next steps:

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