test(miner): add purgeByRepo to attempt-cli's inline WorktreeAllocator fake

Follow-up to the worktree-allocator purge-cli fix: the interface's new required
method broke this test file's hand-constructed allocator stub, caught by the root
typecheck (not the miner package's own scoped build, which doesn't see test/unit/**).

Author: galuis116

test/unit/miner-attempt-cli.test.ts

@@ -1508,6 +1508,7 @@ describe("runAttempt (#5132)", () => {
         },
         release: vi.fn(),
         listSlots: () => [],
+        purgeByRepo: vi.fn(() => 0),
         close: vi.fn(),
       }),
       openClaimLedger: () => claimLedger,