Fix usage of rust_cache in CI and CD

[SeaSkyThe]

Description

Looks like we are never using Rust Cache, since the executable never finds Cargo.toml. This PR fixes the target folder used by rust_cache in CI/CD.

You can check any previous CI: https://github.com/spruceid/sprucekit-mobile/actions/runs/23024537471/job/66869108375#step:4:23 to see the error. And compare with the same step in this PR's CI.

Error:

Run Swatinem/rust-cache@v2
Error: The process '/home/runner/.cargo/bin/cargo' failed with exit code 101
    at ExecState._setResult (/home/runner/work/_actions/Swatinem/rust-cache/v2/dist/restore/index.js:9754:25)
    at ExecState.CheckComplete (/home/runner/work/_actions/Swatinem/rust-cache/v2/dist/restore/index.js:9737:18)
    at ChildProcess.<anonymous> (/home/runner/work/_actions/Swatinem/rust-cache/v2/dist/restore/index.js:9631:27)
    at ChildProcess.emit (node:events:524:28)
    at maybeClose (node:internal/child_process:1104:16)
    at ChildProcess._handle.onexit (node:internal/child_process:304:5) {
  commandFailed: {
    command: 'cargo metadata --all-features --format-version 1 --no-deps',
    stderr: '\x1B[1m\x1B[91merror\x1B[0m: could not find `Cargo.toml` in `/home/runner/work/sprucekit-mobile/sprucekit-mobile` or any parent directory\n'
  }

[sbihel]

Looks good. I don't know why it wasn't already the case but these changes make sense.

Now, if you encounter cache misses, it's probably because the cache limit of 10GB is too little. We can increase it if need be.