[tmm]

tmm's defaults decision, made as he asked:

• ZeroOptions::hidden_disconnect_delay_ms defaults to 300,000 ms (5 minutes), as JS's hiddenTabDisconnectDelay does (DEFAULT_DISCONNECT_HIDDEN_DELAY_MS in zero.ts). Before, it was 0, which disconnected as soon as set_visible(false) was called. The field's doc comment tells mobile apps to set 0 to keep that behaviour, as Swift does.
• Memory stays the default storage. PARITY.md now calls this the one deliberate difference from JS's defaults: SQLite is the opt-in sqlite feature, so the default build has no third-party dependencies, and the app chooses where its replica lives.

Changeset: zero-rust minor. A changed default is a behaviour change, and before 1.0 a breaking change bumps the minor version, as 0.2.0 did. The next release is 0.3.0.

Test: tests/visibility.rs uses default options. A hidden client is still connected after 299 s, with pings answered, and disconnected at 300 s. With the old 0 default it fails at the first assertion; I checked by reverting the default. The conformance vectors set the delay themselves, so nothing else tests Rust's own default.

Nothing else depends on the default: no app calls set_visible, and the conformance runner already passes JS's 300,000.

Checked locally:

• cargo fmt --check and cargo clippy --workspace --all-targets --all-features -D warnings
• cargo test --workspace --all-features and cargo doc -D warnings
• conformance: 66,384 cases, 0 failures, 2,254 under the documented exceptions
• oxfmt --check