[Divyansh151005]

Fixes #648

What this does

• UnescapeError::BadEscape becomes { reason, offset } (breaking API, as discussed on the issue). Display includes the byte offset into the literal token.
• TextDecoder::read_string / read_bytes add that offset to tok.pos before computing line/column, so adjacent literals no longer report errors at the first quote.
• Tests cover direct unescape_str on a two-literal token and decode_from_str on the issue-shaped input.

Testing

rustc 1.95.0 (rust-toolchain.toml)
cargo fmt --check
cargo clippy -p buffa --features text -- -D warnings
cargo test -p buffa --features text unescape
cargo test -p buffa --features text second_concatenated

All passed locally.

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}