Make template assertions newline agnostic

[dajiaohuang]

Summary

• Normalize rendered template line endings in assertions so tests pass with Windows core.autocrlf=true.
• Keep production rendering behavior unchanged.

Validation

• cargo test --manifest-path ci/Cargo.toml --workspace --all-targets --all-features --locked
• cargo fmt --manifest-path ci/Cargo.toml --all --check
• cargo clippy --manifest-path ci/Cargo.toml --workspace --all-targets --all-features --locked -- -D warnings
• render --skip-deprecated against all catalog entries

[mre]

Could we use str::lines() at the affected assertions instead of normalizing the whole rendered string? It handles both LF and CRLF. For the source assertion, we could use rendered.lines().any(|line| line == expected), with expected = format!("Source: {source}"). For the multiline renderer assertions, collecting the lines and checking adjacent windows() would let us keep asserting the blank lines needed between HTML and Markdown without depending on line endings. No extra dependency or helper needed.

[dajiaohuang]

Implemented the requested newline-agnostic assertions in 058d671: source checks now use str::lines(), and the renderer tests collect lines and use adjacent windows() for the required blank-line structure. Validation: git diff --check, cargo fmt --check for both crates, targeted pr-check test (1 passed), and render deprecated tests (3 passed). CI checks are pending.

[mre]

Thanks!