## Description

Make help flag detection more robust by doing it after tokenisation, so
that the help flag is treated consistently like other `--commands` or
`-f`lags.

This PR also introduces a new notion of a `-f`lag to the lexer (which is
only used for `-h` at the moment).

## Test Plan

New unit tests:

```
crates/sui$ cargo nextest run -- lexer
```

Trying the command:

```
sui$ cargo run --bin sui -- --help
sui$ cargo run --bin sui -- -h
```