Add support for oxfmt formatter (#382)

## Summary

- Add oxfmt (Oxc Formatter) as a new formatter option for JavaScript and
TypeScript files

## Details

[Oxfmt](https://oxc.rs/docs/guide/usage/formatter) is a Rust-powered,
Prettier-compatible code formatter from the Oxc project. It's currently
in alpha but offers significant performance improvements (30x+ faster
than Prettier).

Key points:
- Uses `inplace` mode since oxfmt doesn't support stdin/stdout
- Works with all common JS/TS extensions (.js, .jsx, .mjs, .cjs, .ts,
.tsx, .mts)
- Not added to `apheleia-mode-alist` - users can opt-in by setting
`apheleia-formatter` to `oxfmt`
- Defaults are already sensible: 2-space indent, printWidth 100, no tabs

Example usage:
```elisp
(setf (alist-get 'oxfmt apheleia-formatters)
      '("apheleia-npx" "oxfmt" inplace))

;; To use for JS/TS files:
(setq-default apheleia-formatter 'oxfmt)
;; Or per-mode:
(setf (alist-get 'typescript-ts-mode apheleia-mode-alist) 'oxfmt)
```

5 files changed, 17 insertions, 0 deletions

diff --git a/test/formatters/installers/oxfmt.bash b/test/formatters/installers/oxfmt.bash
new file mode 100644
index 0000000..7c33fd0
--- /dev/null
+++ b/test/formatters/installers/oxfmt.bash
@@ -0,0 +1 @@
+npm install -g oxfmt
diff --git a/test/formatters/samplecode/oxfmt/in.js b/test/formatters/samplecode/oxfmt/in.js
new file mode 100644
index 0000000..fd56713
--- /dev/null
+++ b/test/formatters/samplecode/oxfmt/in.js
@@ -0,0 +1,4 @@
+function HelloWorld({greeting = "hello", greeted = '"World"', silent = false, onMouseOver,}) {
+
+  if(!greeting){return null};
+  }
diff --git a/test/formatters/samplecode/oxfmt/in.ts b/test/formatters/samplecode/oxfmt/in.ts
new file mode 100644
index 0000000..c75d40f
--- /dev/null
+++ b/test/formatters/samplecode/oxfmt/in.ts
@@ -0,0 +1 @@
+interface GreetingSettings{greeting: string; duration?: number; color?: string;}declare function greet(setting: GreetingSettings): void;
diff --git a/test/formatters/samplecode/oxfmt/out.js b/test/formatters/samplecode/oxfmt/out.js
new file mode 100644
index 0000000..ca6d896
--- /dev/null
+++ b/test/formatters/samplecode/oxfmt/out.js
@@ -0,0 +1,5 @@
+function HelloWorld({ greeting = "hello", greeted = '"World"', silent = false, onMouseOver }) {
+  if (!greeting) {
+    return null;
+  }
+}
diff --git a/test/formatters/samplecode/oxfmt/out.ts b/test/formatters/samplecode/oxfmt/out.ts
new file mode 100644
index 0000000..143b5a7
--- /dev/null
+++ b/test/formatters/samplecode/oxfmt/out.ts
@@ -0,0 +1,6 @@
+interface GreetingSettings {
+  greeting: string;
+  duration?: number;
+  color?: string;
+}
+declare function greet(setting: GreetingSettings): void;