Add test to compare SSZ bounds against Teku impl (#6836)

* Add test to compare SSZ bounds against Teku impl

Ensure that our SSZ bounds are computed the same way as in Teku by
comparing the bounds for `deneb.SignedBeaconBlock`.

* Lint

* Make platform agnostic regarding how Git checks out newlines

AllTests-mainnet.md

@@ -875,6 +875,11 @@ OK: 2/2 Fail: 0/2 Skip: 0/2
 + Accelerated shuffling computation (with epochRefState jump)                                OK
 ```
 OK: 2/2 Fail: 0/2 Skip: 0/2
+## Size bounds
+```diff
++ SignedBeaconBlockDeneb                                                                     OK
+```
+OK: 1/1 Fail: 0/1 Skip: 0/1
 ## Slashing Interchange tests  [Preset: mainnet]
 ```diff
 + Slashing test: duplicate_pubkey_not_slashable.json                                         OK
@@ -1144,4 +1149,4 @@ OK: 2/2 Fail: 0/2 Skip: 0/2
 OK: 9/9 Fail: 0/9 Skip: 0/9
 
 ---TOTAL---
-OK: 777/782 Fail: 0/782 Skip: 5/782
+OK: 778/783 Fail: 0/783 Skip: 5/783

tests/test_eth2_ssz_serialization.nim

@@ -1,5 +1,5 @@
 # beacon_chain
-# Copyright (c) 2018-2024 Status Research & Development GmbH
+# Copyright (c) 2018-2025 Status Research & Development GmbH
 # Licensed and distributed under either of
 #   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
@@ -9,9 +9,11 @@
 {.used.}
 
 import
+  std/strutils,
   unittest2,
-  ../beacon_chain/spec/datatypes/[phase0, altair],
-  ../beacon_chain/spec/eth2_ssz_serialization
+  ../beacon_chain/spec/datatypes/[phase0, altair, bellatrix, deneb],
+  ../beacon_chain/spec/eth2_ssz_serialization,
+  ./consensus_spec/os_ops
 
 static:
   doAssert isFixedSize(Slot) == true
@@ -49,3 +51,60 @@ suite "Specific field types":
     testit(phase0.TrustedSignedBeaconBlock)
     testit(altair.SignedBeaconBlock)
     testit(altair.TrustedSignedBeaconBlock)
+
+suite "Size bounds":
+  test "SignedBeaconBlockDeneb":
+    # https://gist.github.com/tbenr/a0ae19fe7496106886ec1f3cc097c208
+    template sourceDir: string = currentSourcePath.rsplit(DirSep, 1)[0]
+    let expected = os_ops.readFile(
+      sourceDir/"test_files"/"SszLengthBounds_SignedBeaconBlockDeneb.txt")
+
+    var
+      res = ""
+      loc = @["SignedBeaconBlockDeneb"]
+    func record(T: typedesc) =
+      when T is SomeSig|ValidatorPubKey:
+        res.add loc.join(".") & "[" & $T.blob.len & "]: SszLengthBounds" &
+          "{min=" & $T.minSize & ", max=" & $T.maxSize & "}\n"
+        loc[^1].add "[element]"
+        byte.record()
+      elif T is ExecutionAddress|BloomLogs:
+        res.add loc.join(".") & "[" & $T.data.len & "]: SszLengthBounds" &
+          "{min=" & $T.minSize & ", max=" & $T.maxSize & "}\n"
+        loc[^1].add "[element]"
+        byte.record()
+      elif T is KzgCommitment:
+        res.add loc.join(".") & "[" & $T.bytes.len & "]: SszLengthBounds" &
+          "{min=" & $T.minSize & ", max=" & $T.maxSize & "}\n"
+        loc[^1].add "[element]"
+        byte.record()
+      elif T is array|HashArray:
+        res.add loc.join(".") & "[" & $T.len & "]: SszLengthBounds" &
+          "{min=" & $T.minSize & ", max=" & $T.maxSize & "}\n"
+        loc[^1].add "[element]"
+        ElemType(T).record()
+      elif T is List|HashList:
+        res.add loc.join(".") & "(" & $T.maxLen & "): SszLengthBounds" &
+          "{min=" & $T.minSize & ", max=" & $T.maxSize & "}\n"
+        loc[^1].add "(element)"
+        ElemType(T).record()
+      elif T is BitArray:
+        res.add loc.join(".") & "[" & $T.bits & "]: SszLengthBounds" &
+          "{min=" & $T.minSize & ", max=" & $T.maxSize & "}\n"
+        res.add loc.join(".") & "[element]: SszLengthBounds" &
+          "{min=0(+1 bits), max=0(+1 bits)}\n"
+      elif T is BitList:
+        res.add loc.join(".") & "(" & $T.maxLen & "): SszLengthBounds" &
+          "{min=" & $T.minSize & ", max=" & $T.maxSize & "}\n"
+        res.add loc.join(".") & "(element): SszLengthBounds" &
+          "{min=0(+1 bits), max=0(+1 bits)}\n"
+      else:
+        res.add loc.join(".") & ": SszLengthBounds" &
+          "{min=" & $T.minSize & ", max=" & $T.maxSize & "}\n"
+        when T is object and T isnot Eth2Digest|UInt256:
+          T.enumAllSerializedFields():
+            loc.add fieldName
+            record(FieldType)
+            discard loc.pop()
+    record deneb.SignedBeaconBlock
+    check res.splitLines() == expected.splitLines()