perf(#397): reduce ledger storage footprint of pf_alloc_admin_override

[CollinsC1O]

perf(#397): reduce ledger storage footprint of pf_alloc_admin_override

What

pf_alloc_admin_override no longer takes the PlatformFeeAllocationLock
re-entrancy guard around its write.

Before: set(Lock, true) → set(PlatformFeeAllocation, …) → set(Lock, false)
— 2 distinct instance keys written, 3 set ops.

After: a single set(PlatformFeeAllocation, …) — 1 key written, 1 set op.

Why

The guarded body is one unconditional set with no token transfers or
cross-contract calls between validation and the write, so there is no
re-entrancy window for the lock to protect. The lock writes were pure overhead.

All read-only preconditions are unchanged (require_admin, current.locked
check, assert_platform_fee_allocation_not_locked,
assert_emergency_pause_not_locked, validate_fee_allocation), and the
observable result — allocation replaced and unlocked — is identical.
set_platform_fee_allocation / lock_platform_fee_allocation are untouched.

Tests

• test_pf_alloc_admin_override_writes_single_storage_key — clears the guard
  key, runs the override, asserts it stays absent while the allocation updates
  (proves 1 distinct key written, down from 2).
• test_pf_alloc_admin_override_preserves_lock_guards — PlatformFeeAllocationLock
  and EmergencyPauseLock still block the call; locked allocation not mutated.
• test_pf_alloc_admin_override_failure_path_writes_nothing — invalid ratio
  rejected before any write.

Verification

• cargo test → 460 passed, 0 failed (all existing tests unchanged)
• cargo build --release --target wasm32-unknown-unknown → ok
• cargo fmt --check clean, cargo clippy no new warnings

Closes #397

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