feat(hw/rtl): implement full Top-K CAM search pipeline with serial result output

- add TOPK_K, FIFO_DEPTH, RESULT_SERIAL parameters to cam_params
- add candidate_fifo: synchronous ready/valid FIFO for (row, score) candidates
- add topk_tracker: tracks top-K candidates with clear/ready handshake
- add result_serializer: serializes packed Top-K array into rank-ordered stream
- refactor match_engine_pipeline from 4-state to 8-state Top-K pipeline
- extend cam_top with serial Top-K interface (result_rank/row/score/last)
- add backward-compatible top1_index/top1_score aliases from rank-0 beat
- add comprehensive tests for all new modules

hw/sim/tests/modules/match_engine_pipeline/Makefile

@@ -6,4 +6,24 @@ TOPLEVEL := match_engine_pipeline
 COCOTB_TEST_MODULES := tests.modules.match_engine_pipeline.test_match_engine_pipeline
 VERILOG_SOURCES := $(RTL_MATCH_ENGINE)
 
+# Allow override from command line (e.g. make TOPK_K=1)
+TOPK_K ?= 4
+EXTRA_ARGS += +define+TOPK_K=$(TOPK_K)
+export TOPK_K
+
+# Parameter-specific build directory so K variants never collide.
+SIM_BUILD := sim_build/k_$(TOPK_K)
+
 include $(SIM_ROOT)/mk/cocotb-common.mk
+
+# ── K-specific test targets ──────────────────────────────────────────────
+# Recompile with K=1 and filter to the K=1 test.
+.PHONY: test-k1
+
+test-k1:
+	$(MAKE) -B -f Makefile results.xml TOPK_K=1 \
+	  COCOTB_TEST_FILTER=match_engine_topk_k1
+
+# Also remove all module-local build artifacts, including legacy and variant dirs.
+clean::
+	rm -rf sim_build