[dajiaohuang]

Preserve equals signs in loader argument values

Key Changes:

• Preserve the complete value in joined flags such as
  --package=offline-demo==1.2 by splitting only the first equals sign.
• Apply the same parsing behavior to runtime and build arguments.

Added:

• Regression tests for joined and separated flags with multiple equals signs.

Changed:

• Limit the flag-name/value split to one separator.

Validation:

• Both new regressions fail against the original parser.
• Python 3.12.3 on Ubuntu: ruff check dyana passed.
• mypy --ignore-missing-imports --no-error-summary dyana passed.
• pytest dyana: 191 passed.
• Python 3.10 and 3.11 were not run locally.