Do we really need to wrap `Arc` with `Cow` inside RoTxnInner?

[Logarithmus]

@Kerollmops

Cow in Rust is mainly used for strings. Arc is trivially cloneable on the other hand, so it makes no sense to have sometimes Arc, sometimes &Arc.

heed/heed/src/txn.rs

Line 59 in fdd105d

env: Cow<'e, Arc<EnvInner>>,

This Cow pollutes RoTxnInner, RoTxn and all other code using those structs with lifetimes.

I suggest changing this

struct RoTxnInner<'e> {
    /// Makes the struct covariant and !Sync
    pub(crate) txn: Option<NonNull<ffi::MDB_txn>>,
    env: Cow<'e, Arc<EnvInner>>,
}

to this

struct RoTxnInner {
    /// Makes the struct covariant and !Sync
    pub(crate) txn: Option<NonNull<ffi::MDB_txn>>,
    env: Arc<EnvInner>,
}

[Kerollmops]

Hey @Logarithmus 👋

Interesting, as it is something internal it will not impact users. Would you mind proposing a PR, please?

Have a nice day 🌵