refactor: Centralize configuration resolution funnel (#11727)
## Summary
Introduce a single configuration resolution funnel for CLI + shim paths
and use a fix for `noUpdateNotifier` handling from `turbo.json` as
proof-of-concept.
## Changes
- Added `crates/turborepo-lib/src/config/funnel.rs` as the canonical
entrypoint for resolving configuration from CLI args and shim inputs.
- Switched `CommandBase::load_config` and shim `ConfigProvider` to use
the shared funnel.
- Added `TurborepoConfigBuilder::with_override_config` so one
top-priority override layer can be applied cleanly.
- Fixed mapping of `noUpdateNotifier` from parsed `turbo.json` into
`ConfigurationOptions`.
- Added targeted tests for `no_update_notifier` and CLI override
precedence.
## Testing
- `cargo test -p turborepo-config test_no_update_notifier --
--nocapture`
- `cargo test -p turborepo-lib config::funnel::tests:: -- --nocapture`
## Notes
This is intentionally incremental and establishes the centralized funnel
surface for subsequent migration work across remaining scattered
config/flag/env reads.
