Simplify documentation and QoS configuration

[s2015-turtle]

Summary

• simplify the public README by removing internal transport and protocol details
• replace numeric CAN communication-type terminology with user-facing descriptions
• shorten duplicated configuration examples and package architecture notes
• remove the deprecated can_qos_depth alias and accept only can_rx_qos_depth
• remove the logger dependency that existed only for the deprecation warning
• run feature-branch CI through pull_request only while retaining post-merge push CI on main

Motivation

The README mixed user instructions with internal implementation details, making
the supported configuration and normal operating behavior harder to identify.
The repository has not completed its first rosdistro release, so retaining the
old QoS parameter alias adds ambiguity without providing meaningful release
compatibility.

Validation

• git diff --check
• confirmed that can_qos_depth and legacy_qos no longer occur in tracked implementation or documentation files
• confirmed all parse_driver_configuration declarations and call sites use the updated signature
• local build was intentionally not run; the existing GitHub Actions matrix will validate Humble, Jazzy, Kilted, Lyrical, and Rolling