Add OXC.Format — oxfmt NIF bindings

[dannote]

Prettier-compatible JS/TS formatter via oxfmt, ~30× faster than Prettier.

API

OXC.Format.format!("const   x=1;let   y =  2;", "test.js")
# "const x = 1;\nlet y = 2;\n"

OXC.Format.format!("const x = 1;", "test.js", semi: false)
# "const x = 1\n"

OXC.Format.format!(source, "test.js", sort_imports: true, single_quote: true)

All oxfmt options supported: print_width, tab_width, use_tabs, semi,
single_quote, jsx_single_quote, trailing_comma, bracket_spacing,
bracket_same_line, arrow_parens, end_of_line, quote_props,
single_attribute_per_line, object_wrap, experimental_operator_position,
experimental_ternaries, embedded_language_formatting, sort_imports
(bool or map with sub-options), sort_tailwindcss (bool or map with sub-options).

Implementation

• Separate oxc_fmt_nif crate (same pattern as oxc_lint_nif) — git dep on oxc_formatter since it's not on crates.io
• Reads BEAM terms directly via Term::map_get with pre-declared atoms, no serde
• 19 tests