Bump panda-rs version to 0.49

[jamcleod]

This upgrades the PANDA_PATH and PANDA_PLUGIN_DIR search for Rust plugins, fixes #1438

[jamcleod]

See also: panda-re/panda-rs@4b3b950

I couldn't find any information on reproducing #1438 so while some minor testing makes these changes seem fine, I would like if we could confirm something that didn't work before now does

[AndrewQuijano]

Could we update inventory to 2.0.0?
https://github.com/panda-re/panda-rs/blob/master/panda-rs/Cargo.toml#L38

It says we should update from inventory 0.1.11 to 2.0.0

https://github.com/panda-re/panda/security/dependabot/21
https://github.com/panda-re/panda/security/dependabot/22

[jamcleod]

I'll push a version 0.49.1 that updates inventory separately from this PR. don't need to block this PR on that, as semver will allow the new version to take precedence.

I'll also note that none of how we use inventory are affected by those issues, so it's a non-issue in practice.