fix: preserve markdown tables when pasting into notebooks

[oz-for-oss]

Closes #9747

Summary

• Parse pasted HTML tables into structured Notebook table blocks instead of flattening cells into plain text.
• Route plain-text Notebook Markdown paste through the GFM table parser when Markdown table rendering is enabled.
• Add regression coverage for HTML table parsing with alignment and inline formatting.

Validation

• cargo fmt --manifest-path /workspace/warp/Cargo.toml --all
• cargo test --manifest-path /workspace/warp/crates/markdown_parser/Cargo.toml html_parser
• cargo check --manifest-path /workspace/warp/Cargo.toml -p warp --lib
• cargo clippy --manifest-path /workspace/warp/crates/markdown_parser/Cargo.toml --all-targets --all-features --tests -- -D warnings
• cargo clippy --manifest-path /workspace/warp/Cargo.toml -p warp --lib -- -D warnings

Notes

• Attempted the broader all-target/all-feature Clippy command, but the sandbox lacks libclang, so minimp4-sys failed during bindgen setup before checking this diff.