fw: drop evicted entries from CsLRU location index

[Harsh23Kashyap]

Fixes #210.

Summary

CsLRU.EvictEntries removed the evicted entry from the LRU queue but never deleted its index from the locations map. The erase goes through eraseCsDataFromReplacementStrategy, which does not call BeforeErase, so no other path cleans it up. A forwarder running at content-store capacity leaks one map entry and one orphaned list element per eviction, growing the index without bound for the life of the process.

The fix deletes the evicted index from locations in EvictEntries. This is separate from #154, which tracks buffer allocations in the face link service.

Repro evidence

Go 1.26.6, linux/amd64, ndnd main @ d51682b. CS capacity 5, 100 distinct Data packets inserted.

Regression test against unpatched main:

$ go test ./fw/table/ -run TestCsLRUEvictionForgetsLocations -v
=== RUN   TestCsLRUEvictionForgetsLocations
    cs-lru_test.go:39:
        	Error:      	Not equal:
        	            	expected: 5
        	            	actual  : 100
        	Messages:   	CsLRU.locations keeps stale entries after eviction (memory leak)
--- FAIL: TestCsLRUEvictionForgetsLocations (0.00s)
FAIL
FAIL	github.com/named-data/ndnd/fw/table	0.004s

Same test against this branch:

$ go test ./fw/table/ -run TestCsLRUEvictionForgetsLocations -v
=== RUN   TestCsLRUEvictionForgetsLocations
--- PASS: TestCsLRUEvictionForgetsLocations (0.00s)
PASS
ok  	github.com/named-data/ndnd/fw/table	0.004s

Testing

• New regression test TestCsLRUEvictionForgetsLocations: fails before the fix, passes after.
• go test ./... - all 22 packages pass.
• go vet ./fw/... and gofmt clean.