Fix masterror-derive publish by adding README

[RAprogramm]

Summary

• add a crate-local README for masterror-derive so cargo publish validates the readme key
• bump masterror to 0.10.6 and masterror-derive to 0.6.2, updating the changelog and root README guidance

Testing

• cargo +nightly fmt --
• cargo +1.90.0 clippy -- -D warnings
• cargo +1.90.0 build --all-targets
• cargo +1.90.0 test --all
• cargo +1.90.0 doc --no-deps
• cargo deny check
• cargo audit

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https://chatgpt.com/codex/tasks/task_e_68ceaf165738832bb4de189318e21ed7