standards: add proxy and timelock primitives

[HDauven]

Part 6 of the Dusk standards stack.

Adds proxy, upgrade, and timelock primitives plus the proxy reference contract:

• proxy state store
• upgrade admin with delay and rollback window
• timelock scheduler
• timelock controller self-governance model
• proxy counter Forge reference contract
• focused VM coverage for the proxy reference contract signed admin paths

Tracking:

• Standard tracker: Track proxy, upgrade, and timelock standards #50

Review focus:

• upgrade preparation/activation/cancel/finalize/rollback semantics
• admin authorization envelope binding
• timelock self-governed delay changes
• state-store namespacing and partial-state failure behavior
• Forge reference contract VM behavior

Validation:

• cargo +nightly-2026-02-27 test -p dusk-contract-standards --test proxy_timelock
• make -C standards/examples/proxy_counter wasm
• cargo +nightly-2026-02-27 test -p dusk-contract-standards --test proxy_reference_vm -- --ignored --nocapture
• make standards-ci