fix: remove assert when producing block for new onchain account

[mFragaBA]

when running integration tests for onchain accounts we stumbled upon this error:

thread 'tokio-runtime-worker' panicked at store/src/db/sql.rs:176:17:
assertion failed: account.is_new()
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
2024-04-10T17:43:27.830234Z  INFO write_block_to_db: miden-store: store/src/db/mod.rs:290: close, time.busy: 418µs, time.idle: 18.3µs
2024-04-10T17:43:27.830332Z ERROR apply_block: miden-store: store/src/db/mod.rs:275: error: SQLite pool interaction task failed: Apply block task failed: Panic
2024-04-10T17:43:27.830331Z ERROR store:apply_block:apply_block: miden-store: store/src/state.rs:107: error: Block applying was broken because of closed channel on database side: channel closed

The culprit is the check:

Some(AccountDetails::Full(account)) => {
                debug_assert!(account.is_new());
                ...

The issue with this check is that whenever we submit a transaction from a new account we're already making the account nonce = 1 (could be > 1 once we enable multiple transactions for an account in a single block), but since it's the first transaction we submit to the node a Full account details is created.

[bobbinth]

Looks good! Thank you!