Fix logical bugs in adu-shell script execution (issue #766)

[Nox-MSFT]

Summary

Fixes the logical bugs in adu-shell's Script::Execute() reported in #766, additionally restores file ownership after execution, and surfaces the resulting failures to IoT Hub as meaningful extended result codes.

Bug fixes (src/adu-shell/src/script_tasks.cpp)

Issue #766 identified three logical mistakes in Execute():

1. A missing file was still executed. A failed stat() only skipped the permission/ownership block, but the child process was launched unconditionally afterward. It now logs a "file not found" error and returns the new ADUSHELL_EXIT_FILE_NOT_FOUND without executing.
2. filePermissionsChanged was set in the wrong branch. It was set to true only when chmod failed, so successfully-changed permissions were never restored. It is now set after a successful chmod.
3. The "restore" re-applied the new permissions. Cleanup called chmod(path, mode) with the new exec mode rather than the original. The original mode (captured up front) is now restored.

In addition, the original ownership is now restored after execution (previously the code permanently changed ownership and never restored it). Ownership is restored before permissions, because chown() clears the set-user-ID/set-group-ID bits.

Meaningful extended result codes

Previously any non-zero adu-shell exit code was reported to IoT Hub through the generic ADUC_ERC_SCRIPT_HANDLER_CHILD_PROCESS_FAILURE_EXITCODE(exitCode) wrapper, so e.g. a missing script surfaced as an opaque 0x3050100x value.

The script step handler now maps adu-shell's reserved sentinel exit codes to dedicated, documented ERCs:

adu-shell exit code	ExtendedResultCode	Value
ADUSHELL_EXIT_FILE_NOT_FOUND (6)	ADUC_ERC_SCRIPT_HANDLER_EXECUTE_PRIMARY_FILE_NOT_FOUND	0x3050044C
ADUSHELL_EXIT_BAD_FILE_PERMS (4)	ADUC_ERC_SCRIPT_HANDLER_EXECUTE_SET_PERMISSIONS_FAILURE	0x3050044D
ADUSHELL_EXIT_BAD_FILE_OWNERSHIP (5)	ADUC_ERC_SCRIPT_HANDLER_EXECUTE_SET_OWNERSHIP_FAILURE	0x3050044E
ADUSHELL_EXIT_UNSUPPORTED (3)	ADUC_ERC_SCRIPT_HANDLER_EXECUTE_UNSUPPORTED_ACTION	0x3050044F

A script's own (non-sentinel) exit code still uses the generic child-process wrapper. The new codes are defined in scripts/error_code_generator_defs/result_codes.json (the source of truth) and the generated src/inc/aduc/result.h.

Tests

Added Catch2 unit tests in src/adu-shell/tests/adushell_ut.cpp covering:

• a missing script file is not executed and reports a failure exit status;
• the original file permissions are restored after execution;
• ownership is left unchanged when the configured user/group cannot be resolved (the path the unit-test build actually exercises).

The new tests and the pre-existing script-execute test now write to a unique per-run scratch directory under the build's configurable work folder (ADU_SHELL_TEST_TMP_DIR, derived from ADUC_TMP_DIR_PATH / --work-folder) with RAII cleanup, instead of a hardcoded /tmp path that may be unavailable.

Notes

• adu-shell's process exit code is overloaded: it is either one of the reserved sentinel codes above or the customer script's own exit code. A script that genuinely exits with 3–6 will therefore be labeled with the corresponding sentinel ERC. This ambiguity is pre-existing and is documented in a code comment alongside the translation.
• Related to Download function returns SUCCESS after deleting file it should have downloaded. #765 (file deletion on hash mismatch): not executing a missing file avoids a confusing downstream error, but Download function returns SUCCESS after deleting file it should have downloaded. #765 itself remains a separate issue.

Fixes #766