[refactor] Finalize root FieldsBuilder only when it is not finalized (#3288)
[refactor] Finalize root FieldsBuilder only when it is not finalized (#3288)

* [refactor] Finalize root FieldsBuilder only when it is not finalized

* fix

* fix

* Auto Format

Co-authored-by: Taichi Gardener <52844ac7498fba84f633481a7c3ae54491811c81@gmail.com>
yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi