Disable vid reuse

In several places, the full free vid list is being copied - at block
height 3.5m, there would be 26m entries in the list (and growing)
leading to the list taking more time than the rest of the processing.

Also, rocksdb documentation mentions performance benefits of inserting
already-sorted keys - this seems like a a loose argument for using
ever-increasing vid numbers.

~3x-6x perf improvement depending on where in the block history we are.

pre:
```
INF 2024-06-02 08:26:40.721+02:00 Imported blocks
blockNumber=3500001 txs=1498120 gas=8890837 bps=28.796 tps=320.649
gps=1150.022 avgBps=29.002 avgTps=434.486 avgGps=2578.528
elapsed=57m28s28ms67us160ns
```

post:
```
INF 2024-06-02 21:37:12.146+02:00 Imported blocks
blockNumber=3500001 blocks=100000 txs=1498120 gas=8890837 bps=155.409
tps=1730.486 gps=6206.475 avgBps=120.526 avgTps=1805.623
avgGps=10715.761 elapsed=13m49s697ms
```

nimbus/db/aristo/aristo_init/rocks_db.nim

@@ -147,7 +147,14 @@ proc getIdgFn(db: RdbBackendRef): GetIdgFn =
         return ok w           # Compiler error with `ok(EmptyVidSeq)`
 
       # Decode data record
-      data.deblobify seq[VertexID]
+      # TODO vid reuse disabled, implementation too slow since list could have
+      #      millions of entries
+      data.deblobify(seq[VertexID]).map(proc (v: seq[VertexID]): seq[VertexID] =
+        if v.len > 1:
+          @[v[^1]]
+        else:
+          v
+      )
 
 proc getLstFn(db: RdbBackendRef): GetLstFn =
   result =

nimbus/db/aristo/aristo_vid.nim

@@ -45,19 +45,6 @@ proc vidFetch*(db: AristoDbRef; pristine = false): VertexID =
   doAssert LEAST_FREE_VID <= result.distinctBase
 
 
-proc vidPeek*(db: AristoDbRef): VertexID =
-  ## Like `new()` without consuming this *ID*. It will return the *ID* that
-  ## would be returned by the `new()` function.
-  ##
-  case db.vGen.len:
-  of 0:
-    VertexID(LEAST_FREE_VID)
-  of 1:
-    db.vGen[^1]
-  else:
-    db.vGen[^2]
-
-
 proc vidDispose*(db: AristoDbRef; vid: VertexID) =
   ## Recycle the argument `vtxID` which is useful after deleting entries from
   ## the vertex table to prevent the `VertexID` type key values small.
@@ -69,10 +56,13 @@ proc vidDispose*(db: AristoDbRef; vid: VertexID) =
       let topID = db.vGen[^1]
       # Only store smaller numbers: all numberts larger than `topID`
       # are free numbers
-      if vid < topID:
+      # TODO vid reuse disabled, implementation too slow since list could grow
+      #      to millions of entries
+      # if vid < topID:
+      #   db.top.final.vGen[^1] = vid
+      #   db.top.final.vGen.add topID
+      if vid == topID - 1: # no gap - can recycle
         db.top.final.vGen[^1] = vid
-        db.top.final.vGen.add topID
-
 
 proc vidReorg*(vGen: seq[VertexID]): seq[VertexID] =
   ## Return a compacted version of the argument vertex ID generator state