Use dep: syntax for dependencies in features.

[waywardmonkeys]

This prevents creating implicit features for them which can be confusing (and duplicates features).

[waywardmonkeys]

This drastically improves what is shown when using cargo add.

Before:

❯ cargo init && cargo add miette
    Creating binary (application) package
note: see more `Cargo.toml` keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
    Updating crates.io index
      Adding miette v7.2.0 to dependencies
             Features:
             + derive
             + miette-derive
             - backtrace
             - backtrace-ext
             - fancy
             - fancy-base
             - fancy-no-backtrace
             - fancy-no-syscall
             - no-format-args-capture
             - owo-colors
             - serde
             - supports-color
             - supports-hyperlinks
             - supports-unicode
             - syntect
             - syntect-highlighter
             - terminal_size
             - textwrap
    Updating crates.io index
     Locking 11 packages to latest compatible versions

After:

❯ cargo init && cargo add miette --path ../miette
    Creating binary (application) package
note: see more `Cargo.toml` keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
      Adding miette (local) to dependencies
             Features:
             + derive
             - fancy
             - fancy-base
             - fancy-no-backtrace
             - fancy-no-syscall
             - no-format-args-capture
             - serde
             - syntect-highlighter
    Updating crates.io index
     Locking 11 packages to latest compatible versions

[waywardmonkeys]

@zkat Hello, just wondering if you could please take a look at this PR and the other couple that I have open?