Move dependencies to external

I undid this recently in the hope that bundling everyhting together will
somehow help the perf (perhaps by better minification), but it had the
opposite effect, likely because we were bundling all of shiki's
languages and themes that need to be parsed as well.

Before
```sh
$ hyperfine --warmup 3 "git --no-pager log -p -n3 | node build/index.mjs"
Benchmark 1: git --no-pager log -p -n3 | node build/index.mjs
  Time (mean ± σ):     350.0 ms ±   8.1 ms    [User: 634.5 ms, System: 31.8 ms]
  Range (min … max):   341.0 ms … 369.5 ms    10 runs
```

After
```sh
$ hyperfine --warmup 3 "git --no-pager log -p -n3 | node build/index.mjs"
Benchmark 1: git --no-pager log -p -n3 | node build/index.mjs
  Time (mean ± σ):     308.0 ms ±   2.3 ms    [User: 602.9 ms, System: 25.2 ms]
  Range (min … max):   303.7 ms … 310.4 ms    10 runs
```

scripts/build.mjs

@@ -1,4 +1,5 @@
 import * as esbuild from 'esbuild';
+import fs from 'fs';
 
 /** @type {esbuild.BuildOptions} */
 const commonOptions = {
@@ -7,7 +8,12 @@ const commonOptions = {
     platform: 'node',
     target: 'node18',
     format: 'esm',
-    external: ['benchmark'],
+    external: [
+        'benchmark',
+        ...Object.keys(
+            JSON.parse(fs.readFileSync('package.json', 'utf-8')).dependencies
+        ),
+    ],
     banner: { js: '#!/usr/bin/env node' },
     outExtension: { '.js': '.mjs' },
     sourcemap: false,