Fix optimization specific SREM edge case (#527)

Existing test coverage didn't catch a signed remainder overflow
semantics edge case behavior where at least one the operators is being
constant folded by LLVM instead of solc. This PR fixes the SREM
translation bug and adds missing test coverage for division ops with
constants.

Closes #524

---------

Signed-off-by: xermicus <cyrill@parity.io>

crates/integration/contracts/ShlOverflowProbe.yul

@@ -0,0 +1,20 @@
+/// Probe: `shl(256, x)` — LLVM `shl i256 x, 256` is UB; EVM defines SHL with
+/// count >= 256 as 0. revive's `shift_left` adds a switch+phi guard; this
+/// fixture stresses whether it survives O3 const-folding.
+object "ShlOverflowProbe" {
+    code {
+        let size := datasize("ShlOverflowProbe_deployed")
+        codecopy(0, dataoffset("ShlOverflowProbe_deployed"), size)
+        return(0, size)
+    }
+    object "ShlOverflowProbe_deployed" {
+        code {
+            let tag := calldataload(0)
+            let value := calldataload(32)
+            // count = 256, obfuscated so revive can't fold pre-LLVM
+            let count := shl(8, 1)
+            mstore(0, xor(shl(count, value), tag))
+            return(0, 32)
+        }
+    }
+}