Eval cache: fix cache regressions

- Fix eval cache not being persisted in `nix develop` (since #10570)
- Don't attempt to commit cache transaction if there is no active transaction, which will spew errors in edge cases
- Drive-by: trivial typo fix

(cherry picked from commit e764ed31f6)

src/libcmd/installable-value.hh

@@ -66,7 +66,7 @@ struct ExtraPathInfoValue : ExtraPathInfo
 };
 
 /**
- * An Installable which corresponds a Nix langauge value, in addition to
+ * An Installable which corresponds a Nix language value, in addition to
  * a collection of \ref DerivedPath "derived paths".
  */
 struct InstallableValue : Installable

src/libexpr/eval-cache.cc

@@ -95,7 +95,7 @@ struct AttrDb
     {
         try {
             auto state(_state->lock());
-            if (!failed)
+            if (!failed && state->txn->active)
                 state->txn->commit();
             state->txn.reset();
         } catch (...) {

src/nix/develop.cc

@@ -696,6 +696,10 @@ struct CmdDevelop : Common, MixEnvironment
             }
         }
 
+        // Release our references to eval caches to ensure they are persisted to disk, because
+        // we are about to exec out of this process without running C++ destructors.
+        getEvalState()->evalCaches.clear();
+
         runProgramInStore(store, UseLookupPath::Use, shell, args, buildEnvironment.getSystem());
 #endif
     }