Internals: Set fabricated variable lifetimes

Set implicit net and traced coverage var lifetimes. No functional change.

src/V3Coverage.cpp

@@ -199,6 +199,7 @@ class CoverageVisitor final : public VNVisitor {
             AstVar* const varp = new AstVar{fl_nowarn, VVarType::MODULETEMP, trace_var_name,
                                             incp->findUInt32DType()};
             varp->setIgnoreSchedWrite();  // Ignore the increment output, so no UNOPTFLAT
+            varp->lifetime(VLifetime::STATIC_IMPLICIT);
             varp->trace(true);
             m_modp->addStmtsp(varp);
             UINFO(5, "New coverage trace: " << varp);

src/V3LinkDot.cpp

@@ -3285,6 +3285,7 @@ class LinkDotResolveVisitor final : public VNVisitor {
         }
         AstVar* const newp
             = new AstVar{nodep->fileline(), VVarType::WIRE, nodep->name(), VFlagLogicPacked{}, 1};
+        newp->lifetime(VLifetime::STATIC_IMPLICIT);
         newp->trace(modp->modTrace());
         modp->addStmtsp(newp);
         // Link it to signal list, must add the variable under the module;