fix(tvix/nix-compat): Feature flag code only used in async r/8587

When only the wire feature was enabled two methods were unused and so
would faild `cargo check --no-default-features --features wire`.

This feature flags those two methods on async feature since that is the
only place they are used.

Change-Id: I6ec18a670e3c6e3ecee8d1417c99f1a5084e0ae7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12346
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: Brian Olsen <me@griff.name>
Tested-by: BuildkiteCI

0 files changed, 0 insertions, 0 deletions