Merge 'btree: cursor with lineal stack structure' from Pere Diaz Bou

Removed MemPage from the code in favor of an array to encode the stack
of the cursor. This is both simpler and better in terms of memory
access.
O_DIRECT was removed from WAL file as it introduces alignment
constraints that are too hard to follow in regular appends. Maybe in the
future?

Closes #378

.github/workflows/rust.yml

@@ -25,12 +25,15 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-    - uses: Swatinem/rust-cache@v2
     - uses: actions/checkout@v3
+    - uses: Swatinem/rust-cache@v2
     - name: Build
       run: cargo build --verbose
     - name: Test
+      env:
+        RUST_LOG: ${{ runner.debug && 'limbo_core::storage=trace' || '' }}
       run: cargo test --verbose
+      timeout-minutes: 5
 
   build-wasm:
     runs-on: ubuntu-latest