system-requirements can't be target specific.

[ruben-arts]

Checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pixi, using pixi --version.

Reproducible example

[project]
name = "test"
channels = []
platforms = ["osx-arm64", "linux-64"]

[target.linux-64.system-requirements]
cuda = "12.0"

Results in:

  × unknown field `system-requirements`, expected one of `dependencies`, `host-dependencies`, `build-dependencies`, `run-dependencies`, `pypi-
  │ dependencies`, `activation`, `tasks`
   ╭─[pixi.toml:8:28]
 7 │
 8 │ [target.linux-64.system-requirements]
   ·                  ───────────────────
 9 │ cuda = "12.0"
   ╰────

Issue description

This is not implemented correctly, as it should have system requirements here:

pixi/crates/pixi_manifest/src/target.rs

Lines 22 to 38 in 2e8ca9b

	pub struct WorkspaceTarget {
	/// Dependencies for this target.
	///
	/// TODO: While the pixi-build feature is not stabilized yet, a workspace
	/// can have host- and build dependencies. When pixi-build is stabilized, we
	/// can simplify this part of the code.
	pub dependencies: HashMap<SpecType, IndexMap<PackageName, PixiSpec>>,
	/// Specific python dependencies
	pub pypi_dependencies: Option<IndexMap<PyPiPackageName, PyPiRequirement>>,
	/// Additional information to activate an environment.
	pub activation: Option<Activation>,
	/// Target specific tasks to run in the environment
	pub tasks: HashMap<TaskName, Task>,
	}

Expected behavior

Being able to set system requirements per target.