fix: cargo build/install -p resolves target to shader crate

[schell]

These changes fix #121 by separating --package/-p from --shader-crate args and performing a lookup using cargo_metadata to resolve the package name to the shader crate path.

Fixes #121.

[schell]

@tombh it looks like maybe the tests are failing on an old dependency - is this another case where we need to run cargo update or similar?

[tombh]

Here's the error, it's the same for both the 0.8.0 and 0.9.0 job failures:

error: package `indexmap v2.12.0` cannot be built because it requires rustc 1.82 or newer, while the currently active rustc version is 1.71.0-nightly
Either upgrade to rustc 1.82 or newer, or use
cargo update -p indexmap@2.12.0 --precise ver

But I notice that our lockfile has:

[[package]]
name = "indexmap"
version = "2.6.0"

So I can't remember why those old builds might be skipping the lockfile 🤔

[Firestar99]

see #123

[Firestar99]

Looks good, just one minor performance thing

[Firestar99]

Let's merge it as is, even with failing CI. I assume it is ready to review since you asked for one from me, even though the PR itself is still set to WIP.