fix(parser): fix bytecode CJS pragma detection after shebang (#25868)

### What does this PR do?

Fix bytecode CJS pragma detection when source file contains a shebang.

When bundling with `--bytecode` and the source file has a shebang, the
output silently fails to execute (exits 0, no output).

Reproduction:
[github.com/kjanat/bun-bytecode-banner-bug](https://github.com/kjanat/bun-bytecode-banner-bug)

```js
// Bundled output:
#!/usr/bin/env bun           // shebang preserved
// @bun @bytecode @bun-cjs   // pragma on line 2
(function(exports, require, module, __filename, __dirname) { ... })
```

The pragma parser in `hasBunPragma()` correctly skips the shebang line,
but uses `self.lexer.end` instead of `contents.len` when scanning for
`@bun-cjs`/`@bytecode` tokens. This causes the pragma to not be
recognized.

**Fix:**

```zig
// Before
while (cursor < self.lexer.end) : (cursor += 1) {

// After
while (cursor < end) : (cursor += 1) {
```

Where `end` is already defined as `contents.len` at the top of the
function.

### How did you verify your code works?

- Added bundler test `banner/SourceHashbangWithBytecodeAndCJSTargetBun`
in `test/bundler/bundler_banner.test.ts`
- Added regression tests in
`test/regression/issue/bun-bytecode-shebang.test.ts` that verify:
  - CJS wrapper executes when source has shebang
  - CJS wrapper executes when source has shebang + bytecode pragma
- End-to-end: bundled bytecode output with source shebang runs correctly
- Ran the tests in the
[kjanat/bun-bytecode-banner-bug](https://github.com/kjanat/bun-bytecode-banner-bug)
repo to verify the issue is fixed

---------

Signed-off-by: Kaj Kowalski <info@kajkowalski.nl>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

test/bundler/bundler_banner.test.ts

@@ -203,4 +203,33 @@ module.exports = 1;`,
       `);
     },
   });
+
+  itBundled("banner/SourceHashbangWithBytecodeAndCJSTargetBun", {
+    banner: "// Copyright 2024 Example Corp",
+    format: "cjs",
+    target: "bun",
+    bytecode: true,
+    outdir: "/out",
+    minifyWhitespace: true,
+    backend: "api",
+    files: {
+      "/a.js": `#!/usr/bin/env bun
+module.exports = 1;
+console.log("bun!");`,
+    },
+    onAfterBundle(api) {
+      const content = api.readFile("/out/a.js");
+      // Shebang from source should come first, then @bun pragma
+      expect(content).toMatchInlineSnapshot(`
+        "#!/usr/bin/env bun
+        // @bun @bytecode @bun-cjs
+        (function(exports, require, module, __filename, __dirname) {// Copyright 2024 Example Corp
+        module.exports=1;console.log("bun!");})
+        "
+      `);
+    },
+    run: {
+      stdout: "bun!\n",
+    },
+  });
 });