feat(solana): two-step propose/accept for set_access_manager

[mariuszzak]

Summary

set_access_manager was a one-step operation — a single admin call could irreversibly repoint a program to a different Access Manager. If the admin accidentally set it to a wrong or nonexistent AM address, the program would become unrecoverable: all future admin-gated calls (including another set_access_manager to fix the mistake) would fail because require_admin reads roles from the now-invalid AM.

This PR replaces the one-step set_access_manager with a two-step propose/accept pattern across all IBC programs (ICS26, ICS07, GMP, attestation):

• propose_access_manager_transfer — current AM's admin proposes a new AM address (rejects zero-address and self-transfers)
• accept_access_manager_transfer — the new AM's admin accepts, proving it is valid and operational before the switch takes effect
• cancel_access_manager_transfer — current AM's admin cancels a pending proposal

The accept step requires ADMIN_ROLE on the new AM, so the transfer cannot complete unless the target AM is a real, initialized Access Manager with an active admin. This eliminates the risk of bricking a program by pointing it to a bad address.

Shared logic via HasPendingAccessManager trait

Each IBC program's state struct implements a HasPendingAccessManager trait. The actual propose/accept/cancel handlers live in access-manager/src/helpers.rs and are reused by all four programs, avoiding duplicated validation logic.

Programs affected

• ics26-router — RouterState.pending_access_manager
• ics07-tendermint — AppState.pending_access_manager
• ics27-gmp — GMPAppState.pending_access_manager
• attestation — AttestationState.pending_access_manager

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.91%. Comparing base (3a362e3) to head (5c5db78).
⚠️ Report is 1 commits behind head on mariuszzak/upgrade-authority-transfer.

Additional details and impacted files

@@                          Coverage Diff                           @@
##           mariuszzak/upgrade-authority-transfer    #1014   +/-   ##
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  Coverage                                  99.91%   99.91%           
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  Files                                         27       27           
  Lines                                       1123     1123           
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  Hits                                        1122     1122           
  Misses                                         1        1           

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