Let the highest linked host cover its base protocol, re-record next baseline

With core at protocol 28 and no p29 submodule, a vnext build has the p28
host reporting 29, so protocol 28 had no exact linked host and
isProtocolBackedByLinkedSorobanHost rejected it -- failing 70 of 131 [tx]
cases. rs-soroban-env explicitly supports this: Host::maybe_check_protocol_version
bypasses its protocol check under "next" because "a 'next' host can be used
as the current host for both its base protocol and the next one", and
ParsedModule's meta-section check does the same. Accept the highest linked
host for protocolVersion + 1 on that basis.

Restricting it to the highest host keeps fastdev's collapse of historical
protocols onto a newer host detectable, which is what the exact-match rule
is there to catch.

Uncomment moduleCacheProtocolCount -= 1 in "Module cache across protocol
versions", as that test's own comment instructs when the next protocol
points at another copy of the current host: soroban_module_cache.rs routes
29 to p28_cache, so 29 adds no cache of its own.

Re-record test-tx-meta-baseline-next, which recorded protocol 28 and now
records 29. All 131 [tx] cases pass.

Author: sisuresh

src/test/TestUtils.cpp

@@ -47,6 +47,20 @@ isProtocolBackedByLinkedSorobanHost(uint32_t protocolVersion,
         return false;
     }
 
+    // The highest linked host may be a "next" build, which reports one protocol
+    // above its base and is designed to serve both: see the "next" bypasses in
+    // rs-soroban-env's Host::maybe_check_protocol_version ("a 'next' host can
+    // be used as the current host for both its base protocol and the next one")
+    // and in ParsedModule's meta-section check. Accept that host for its base
+    // protocol. Restricting this to the highest host keeps fastdev's collapse of
+    // historical protocols onto a newer host detectable, which is what the
+    // exact-match rule below exists to catch.
+    if (selectedHost + 1 == hostProtocols.end() &&
+        *selectedHost == protocolVersion + 1)
+    {
+        return true;
+    }
+
     // Protocol 20 is serviced by the p21 host. All later Soroban protocols
     // should have their own linked host in non-fastdev builds.
     return protocolVersion == static_cast<uint32_t>(SOROBAN_PROTOCOL_VERSION)

src/transactions/test/InvokeHostFunctionTests.cpp

@@ -7788,7 +7788,9 @@ TEST_CASE("Module cache across protocol versions", "[tx][soroban][modulecache]")
     // work-in-progress next host, in which case there _is_ a separate module
     // cache and the following line of code should be commented-out.
     //
-    // moduleCacheProtocolCount -= 1;
+    // There is no work-in-progress next host right now: soroban_module_cache.rs
+    // directs protocol 29 to p28_cache, so 29 contributes no cache of its own.
+    moduleCacheProtocolCount -= 1;
 #endif
     REQUIRE(app->getLedgerManager()
                 .getSorobanMetrics()