feature(variable sub): substitue variables from other variables

[cedric05]

• works for in file properties
• need it work for property file?
• need it work for properties

fixes #343 #342

This pull request includes various changes to improve the functionality and testing of the Dothttp project. The most important changes include enabling diagnostics and testing configurations in VSCode settings, modifying the property validation logic, updating the project version, adding a new HTTP request test file, and introducing a new test case for property substitution.

Improvements to development environment:

• .vscode/settings.json: Enabled diagnostics and testing configurations for Python and Dothttp.

Enhancements to property validation:

• dothttp/utils/property_util.py: Modified the validate_n_gen method to split properties on the first = sign and resolve property values using a cache.

Project version update:

• pyproject.toml: Updated the project version from 0.0.43a29 to 0.0.43.

New test file for HTTP requests:

• test/extensions/commands/custom-property/property-refer.http: Added a new test file to verify property substitution in HTTP requests.

New test case for property substitution:

• test/extensions/test_commands.py: Added a test case test_property_sub to validate the property substitution logic in HTTP requests.