add history session id to $nu

[fdncred]

Description

This PR adds the reedline history session id to the $nu variable. When using the sqlite history db, this should make it easier to query history records by history session. A new history session is created with every new instance of reedline, so every new instance of nushell.

The history session id is stored at time since UNIX_EPOCH in nanoseconds but is not intended to be used as any type of a timing mechanism. It's just meant to try and have a mostly unique history session id, that fits within the datatype. If we have to move to a ulid, we'll have to change the data type, which we don't really want to do.

This PR is dependent on nushell/reedline#485 so, I'll make this a draft until the reedline PR is landed.

Note: I couldn't get ci to see the right main branch in reedline without specifically pointing it out. Not sure if it was cached or what.

Tests

Make sure you've done the following:

• Add tests that cover your changes, either in the command examples, the crate/tests folder, or in the /tests folder.
• Try to think about corner cases and various ways how your changes could break. Cover them with tests.
• If adding tests is not possible, please document in the PR body a minimal example with steps on how to reproduce so one can verify your change works.

Make sure you've run and fixed any issues with these commands:

• cargo fmt --all -- --check to check standard code formatting (cargo fmt --all applies these changes)
• cargo clippy --workspace --features=extra -- -D warnings -D clippy::unwrap_used -A clippy::needless_collect to check that you're using the standard code style
• cargo test --workspace --features=extra to check that all the tests pass