Implement YAML anchor/alias for streamlined testlist structure

Created by: xiaoweish

Problem Statement The current testlist (e.g., testlist_riscv-compliance-cv32a60x.yaml) contains many duplicate lines, such as gcc_opts and path_var: TESTS_PATH, while this repetition is necessary for each individual test case, it leads to a bloated file size and reduced readability.

Proposed Solution

1. Utilize YAML anchors and aliases to make the testlist YAML file more compact, as described in YAML anchors.
2. Introduce a new keyword testlist in the YAML file.
3. Ensure backward compatibility with the existing implementation.

The proposed changes will make the testlist YAML file more compact and readable.