fix: flush static buffer in conditionals and correct helpers import path

- Flush static buffer at end of each conditional branch (if/else/else-if)
  to ensure content is rendered inside the correct blocks
- Add helpers_path parameter to zig_codegen.generate() for correct
  relative imports in nested directories (e.g., '../helpers.zig')
- Fix build.zig to use correct CLI path (src/tpl_compiler/main.zig)
- Export zig_codegen from root.zig for CLI module usage

Bump version to 0.3.11

build.zig.zon

@@ -1,6 +1,6 @@
 .{
     .name = .pugz,
-    .version = "0.3.10",
+    .version = "0.3.11",
     .fingerprint = 0x822db0790e17621d, // Changing this has security and trust implications.
     .minimum_zig_version = "0.15.2",
     .dependencies = .{},