ci: checkout AdaWorldAPI/ndarray sibling for build + test workflows

ndarray is a custom fork (55 HPC modules, AMX tiles, jitson Cranelift
JIT, 880+ tests) at ../../../ndarray relative to crates/lance-graph/.
CI runners don't have the sibling repo cloned → cargo can't resolve
the path dependency → build/test/clippy all fail.

Fix: add `actions/checkout@v4` step for AdaWorldAPI/ndarray with
`path: ../ndarray` in both rust-test.yml and build.yml. This places
the checkout at $GITHUB_WORKSPACE/../ndarray which resolves correctly
from the crate's Cargo.toml path = "../../../ndarray".

NOT the fix Copilot suggested (replace with crates.io ndarray 0.15).
That would lose the entire HPC foundation.

https://claude.ai/code/session_01SbYsmmbPf9YQuYbHZN52Zh

Author: claude

.github/workflows/build.yml

@@ -30,6 +30,11 @@ jobs:
           - stable
     steps:
       - uses: actions/checkout@v4
+      - name: Checkout AdaWorldAPI/ndarray (sibling dependency)
+        uses: actions/checkout@v4
+        with:
+          repository: AdaWorldAPI/ndarray
+          path: ../ndarray
       - name: Setup rust toolchain
         run: |
           rustup toolchain install ${{ matrix.toolchain }}

.github/workflows/rust-test.yml

@@ -30,6 +30,11 @@ jobs:
           - stable
     steps:
       - uses: actions/checkout@v4
+      - name: Checkout AdaWorldAPI/ndarray (sibling dependency)
+        uses: actions/checkout@v4
+        with:
+          repository: AdaWorldAPI/ndarray
+          path: ../ndarray
       - name: Setup rust toolchain
         run: |
           rustup toolchain install ${{ matrix.toolchain }}
@@ -56,6 +61,11 @@ jobs:
     timeout-minutes: 30
     steps:
       - uses: actions/checkout@v4
+      - name: Checkout AdaWorldAPI/ndarray (sibling dependency)
+        uses: actions/checkout@v4
+        with:
+          repository: AdaWorldAPI/ndarray
+          path: ../ndarray
       - name: Setup rust toolchain
         run: |
           rustup toolchain install stable