Propagate database changes from scripting engine temp client (#2959)

**Problem:** temp client does not preserve db between VM_Call() calls.
SELECT changes the database context of a temporary client created for
that specific call. However, this database change is not propagated back
to the context client, so subsequent commands in the same script will
execute in the wrong database.
Behaviour on unstable:
```
127.0.0.1:6379> eval "server.call('SELECT', '1'); return server.call('SET', 'lua_test', 'incorrect')" 0
OK
127.0.0.1:6379> select 0
OK
127.0.0.1:6379> get lua_test
"incorrect"
127.0.0.1:6379> select 1
OK
127.0.0.1:6379[1]> get lua_test
(nil)
```

Behaviour with fixes:
```
127.0.0.1:6379> eval "server.call('SELECT', '1'); return server.call('SET', 'lua_test', 'correct')" 0
OK
127.0.0.1:6379> select 0
OK
127.0.0.1:6379> get lua_test
(nil)
127.0.0.1:6379> select 1
OK
127.0.0.1:6379[1]> get lua_test
"correct"
```

Signed-off-by: Daniil Kashapov <daniil.kashapov.ykt@gmail.com>

Author: dvkashapov

src/module.c

@@ -6765,6 +6765,12 @@ ValkeyModuleCallReply *VM_Call(ValkeyModuleCtx *ctx, const char *cmdname, const
     }
     call(c, call_flags);
 
+    /* Propagate database changes from the temporary client back to the context client
+     * when running in script mode to make next commands execute in the correct db */
+    if (c && (flags & VALKEYMODULE_ARGV_SCRIPT_MODE) && is_running_script && c->db != ctx->client->db) {
+        ctx->client->db = c->db;
+    }
+
     /* We reset errno here because on macOS some system calls set errno even when
      * they succeed. For instance, certain time-related syscalls may set errno
      * to ETIMEDOUT on successful completion.

src/script.c

@@ -211,6 +211,7 @@ int scriptPrepareForRun(scriptRunCtx *run_ctx,
     run_ctx->original_client = caller;
     run_ctx->funcname = funcname;
     run_ctx->slot = caller->slot;
+    run_ctx->original_db = caller->db;
 
     run_ctx->start_time = getMonotonicUs();
 
@@ -250,6 +251,8 @@ void scriptResetRun(scriptRunCtx *run_ctx) {
         unprotectClient(run_ctx->original_client);
     }
 
+    run_ctx->original_client->db = run_ctx->original_db;
+
     run_ctx->slot = -1;
 
     preventCommandPropagation(run_ctx->original_client);

src/script.h

@@ -77,6 +77,7 @@ struct scriptRunCtx {
     scriptingEngine *engine;
     const char *funcname;
     client *original_client;
+    serverDb *original_db;
     int flags;
     int repl_flags;
     monotime start_time;

tests/unit/scripting.tcl

@@ -2598,4 +2598,38 @@ start_server {tags {"scripting"}} {
             r eval "error({})" 0
         }
     }
+
+    test {EVAL - SELECT inside script affects subsequent commands in same script} {
+        r select 0
+        r del testkey
+        r set testkey "db0_value"
+        
+        # Run script that:
+        # 1. Reads from DB 0
+        # 2. Switches to DB 1
+        # 3. Sets a key in DB 1
+        # 4. Returns the value from DB 1
+        set result [run_script {
+            local db0_val = server.call('get', 'testkey')
+            server.call('select', '1')
+            server.call('set', 'testkey', 'db1_value')
+            return server.call('get', 'testkey')
+        } 1 testkey]
+        
+        # Script returned the DB 1 value
+        assert_equal "db1_value" $result
+        
+        # Verify we're back in DB 0 after script
+        assert_equal "db0_value" [r get testkey]
+        
+        # Verify DB 1 has the new value that was set by the script
+        r select 1
+        assert_equal "db1_value" [r get testkey]
+        
+        # Cleanup
+        r del testkey
+        r select 0
+        r del testkey
+        set _ {}
+    } {} {singledb:skip}
 }