Refactor Makefile and enhance disk/memory eviction tests

- Updated the 'bench' target in the Makefile to run all benchmarks for MemoryFS and DiskFS, improving clarity and coverage.
- Added explicit post-eviction consistency checks in DiskFS tests to ensure on-disk files are removed after eviction.
- Introduced new benchmarks for memory eviction strategies under pressure, enhancing test coverage for memory management.
- Improved error handling in benchmark tests for both disk and memory file systems, ensuring robustness during performance evaluations.
- Refactored key generation in tests for consistency and clarity.

Makefile

@@ -26,12 +26,12 @@ deps: ## Download dependencies
 clean: ## Remove build artifacts and test cache
 	@rm -rf bin/ dist/ *.test coverage.out steamcache2
 
-bench: deps ## Run benchmarks (with timer hygiene + allocs; optional in CI)
-	@echo "Running key benchmarks (use -benchmem for more)..."
-	@go test -bench=BenchmarkMemoryFS_CreateOpen -benchmem -run=^$ ./vfs/memory
-	@go test -bench=BenchmarkDiskFS_CreateOpen -benchmem -run=^$ ./vfs/disk
-	@go test -bench=BenchmarkEvictionUnderPressure -benchmem -run=^$ ./vfs/memory
-	@echo "Bench done. Add -bench=. for all."
+bench: deps ## Run all benchmarks (MemoryFS + DiskFS variants, including all eviction strategies)
+	@echo "Running MemoryFS benchmarks..."
+	@go test -bench=. -benchmem -run=^$ -benchtime=1s ./vfs/memory
+	@echo "Running DiskFS benchmarks..."
+	@go test -bench=. -benchmem -run=^$ -benchtime=1s ./vfs/disk
+	@echo "Bench done."
 
 help: ## Show this help message
 	@echo steamcache2 Makefile