fix: FreeBSD cross-compile type mismatch in diskspace_unix.go

Cast Statfs_t fields (Blocks, Bavail, Bfree) through uint64() for
FreeBSD where they are int64, not uint64 as on Linux/Darwin. Suppress
unconvert lint warnings since the linter runs on Linux where the casts
appear redundant.

Fixes TestCrossPlatformBuild/freebsd_amd64.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mikeakers

.github/workflows/ci.yml

@@ -170,12 +170,12 @@ jobs:
         id: cache-beads-int
         uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5
         with:
-          path: /usr/local/bin/bd
-          key: beads-latest-${{ hashFiles('.github/workflows/ci.yml') }}
+          path: ~/go/bin/bd
+          key: beads-${{ hashFiles('.github/workflows/ci.yml') }}
 
       - name: Install beads (bd)
         if: steps.cache-beads-int.outputs.cache-hit != 'true'
-        run: curl -fsSL https://raw.githubusercontent.com/steveyegge/beads/main/scripts/install.sh | bash
+        run: go install github.com/steveyegge/beads/cmd/bd@v0.57.0
 
       - name: Install gotestsum
         run: go install gotest.tools/gotestsum@latest