fix: restore ephemeral_account and sweep_controller tests for CI

[phertyameen]

What

Fixes the failing Test Contracts CI by restoring the corrupted ephemeral_account test suite and aligning the contract test environments with the standalone network passphrase check enforced by initialize (require_network).

Changes

• ephemeral_account: repaired src/test.rs (was corrupted: unclosed delimiters, undefined variables, mangled assertions); added a test_env() helper that calls env.ledger().set_network_id(...) with the standalone network id so initialize passes require_network.
• shared: added passphrase::standalone_network_id() helper; fixed doc-comment style.
• sweep_controller: converted ephemeral initialize test calls to the 6-arg signature, fixed event-filter assertions and error-code expectations, routed claim through sweep_claim, wrapped migration tests in env.as_contract, and removed unused imports.

Verification

All CI-equivalent checks pass locally (rust 1.92):

• cargo test — ephemeral_account 20/20, sweep_controller 39/39 (4 unrelated integration tests remain ignored with TODO), reserve_contract 20/20
• cargo fmt -- --check — clean across all contract crates
• cargo clippy -- -D warnings (CI-equivalent, lib) — clean