[geroldsteiner67]

Summary

• Rotate the node's on-disk node.log at 64 MiB, retaining three backups.
• Rotate a pre-existing oversized log on the next write, preventing indefinite growth on long-running testnet nodes.
• Cover rotation, backup ordering, and legacy oversized logs with a unit test.

Validation

• cargo check -p modality-node
• cargo clippy -p modality-node -- -D warnings -A clippy::too_many_arguments
• cargo test -p modality-node rotation_tests::bounds_new_and_preexisting_log_files
• RUSTFLAGS="-D warnings" cargo check --all
• RUSTFLAGS="-D warnings" cargo check --all --tests --examples
• cargo clippy --all -- -D warnings -A clippy::too_many_arguments