[pavelzw]

Description

Python builds currently force -vv for both uv and pip, so a normal pixi install prints debug and trace output. Derive installer verbosity from the backend's build logging level instead, using the same behavior for both installers.

Forward Pixi's CLI verbosity through immutable per-dispatcher configuration to spawned JSON-RPC backends, including pixi-build-rattler-build. Normal invocations retain the backend's default logging; -vv enables backend debug logging, -vvv and above enable trace logging, and -q disables build logging. This does not rewrite commands in user-provided recipe scripts.

Adapted from @Jamison929611's #6806, including its updated installer-generic approach requested in review. Strengthens the regression coverage by exercising the actual tracing filter and checking both pip and uv script generation on Unix and Windows, including preservation of extra arguments and editable installs.

Fixes #6099

How Has This Been Tested?

• cargo test --locked -p pixi_build_frontend -p pixi-build-python: 7 frontend tests and 93 Python backend tests passed; 1 ignored.
• cargo test --offline -p pixi-build-python: 93 passed, 1 ignored, after strengthening the logging-filter regression test.
• cargo test --locked -p pixi_command_dispatcher: 176 unit tests and 43 integration tests passed; 2 integration tests and 2 doc tests ignored.
• cargo check --locked -p pixi_cli
• cargo clippy --locked -p pixi_build_frontend -p pixi-build-python -p pixi_command_dispatcher -p pixi_cli --all-targets -- -D warnings
• cargo fmt --all -- --check
• git diff --check

Windows script generation was tested locally; native Windows execution was not tested.

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.

Tools: Codex

Prompt: Fix #6099 after reviewing #6806 and avoiding the installer-specific verbosity issue identified in review; verify how forwarding interacts with pixi-build-rattler-build and create a draft PR.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added sufficient tests to cover my changes.