fix: improve pps capability handling

[IvanLi-CN]

Summary

• add explicit PPS advertisement mode so enabling PPS no longer forces register-backed PPS config
• add structured PD/PPS capability readback helpers for fixed/PPS ranges and current limits
• honor the fast-charge global disable gate across protocol status APIs
• use split register write/read transactions for register reads and update I2C mocks accordingly

Validation

• cargo +stable fmt -- --check
• cargo +stable test
• cargo +stable test --all-features
• cargo +stable clippy --all-targets --all-features -- -D warnings