Add Coveralls integration for PR coverage reports #892

Job	Run time
cargo fmt --all -- --check	15s
Code Coverage (macos-latest, macos)	1m 34s
Code Coverage (windows-latest, windows)	2m 15s
cargo check (windows-latest)	44s
cargo clippy -- -D warnings (macOS-latest)	41s
Code Coverage (ubuntu-latest, unix)	1m 40s
cargo clippy -- -D warnings (windows-latest)	1m 2s
Run the fuzzers	1m 56s
cargo test (ubuntu-latest)	28s
cargo clippy -- -D warnings (ubuntu-latest)	25s
cargo check (macOS-latest)	19s
cargo check (ubuntu-latest)	15s
cargo test (macOS-latest)	31s
Minimum Supported Rust Version (windows-latest)	1m 0s
cargo test (windows-latest)	1m 3s
Minimum Supported Rust Version (macOS-latest)	28s
Minimum Supported Rust Version (ubuntu-latest)	26s
	15m 2s

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