fix: set defaulted_keys in lockfile parsing for both formats (GREEN)

Fix both lockfile parsing implementations to properly set defaulted_keys
with the "_initialized" sentinel required by write_repodata_record().

Changes:
- env_lockfile_conda.cpp: Copy defaulted_keys from from_url() result
- env_lockfile_mambajs.cpp: Set defaulted_keys = {"_initialized"}
  (lockfile data is authoritative, so no fields are "defaulted")

This fix is required after the env_lockfile.cpp refactoring that split
the implementation into separate files for conda and mambajs formats.

Test Status: ALL TESTS PASS (GREEN phase)
- lockfile_packages_have_initialized_in_defaulted_keys-conda: PASSED
- lockfile_packages_have_initialized_in_defaulted_keys-mambajs: PASSED
- All existing tests: PASSED

Tests fixed:
- test_lockfile[condalock-True] (Python integration test that was failing in CI)

Related: #4095

Author: maresb

libmamba/src/core/env_lockfile_conda.cpp

@@ -73,6 +73,10 @@ namespace mamba
                 package.info.channel = maybe_parsed_info->channel;
                 package.info.build_string = maybe_parsed_info->build_string;
                 package.info.platform = maybe_parsed_info->platform;
+                // Copy defaulted_keys for fail-hard verification in write_repodata_record().
+                // The "_initialized" sentinel proves this PackageInfo was properly constructed.
+                // See issue #4095.
+                package.info.defaulted_keys = maybe_parsed_info->defaulted_keys;
             }
 
             for (const auto& dependency : package_node["dependencies"])

libmamba/src/core/env_lockfile_mambajs.cpp

@@ -96,6 +96,11 @@ namespace mamba
                 // chosen channel mirror url
             }
 
+            // Set _initialized sentinel for fail-hard verification in write_repodata_record().
+            // Lockfile data is authoritative, so no fields are "defaulted" - only the sentinel.
+            // See issue #4095.
+            package.info.defaulted_keys = { "_initialized" };
+
             return package;
         }