Merge pull request !7730 from luoyang/c-api-pyfunc

1. Start the child process in the init phase
2. At the beginning of each epoch, the child process is not recreated, but the child process created at the beginning is used

Merge pull request !7618 from guozhijian/add_per_batch_map_usage_in_api

Merge pull request !6645 from liyong126/md_unique_op

Merge pull request !7050 from cathwong/ckw_api_text_examples

Merge pull request !6905 from lixiachen/CacheOp_dev

Merge pull request !5300 from nhussain/slice_op

Merge pull request !6017 from ZiruiWu/per_batch_map_multi_col

Merge pull request !5930 from Jamie/CacheOp_dev

add string implementation, can handle partial string slices

finish core implementation, added Index object

fix up the logic

add in new SliceOption object, cleaning up tests

decided to use project after batch as well

per_batch_map 1->x colunm works

add more test case

add test cases, project after map

col order hahaah

fix ci

add test cases

addr review cmts

ci

fix build err

fix test case failure

ci

Merge pull request !6301 from nhussain/c_py_compose

Leaf ops do self-reset.

embed python compose op

add implicit compose op

more tests

Merge pull request !6588 from yanghaitao/yht_protect_pyfunc_timeout

Merge pull request !6576 from heleiwang/mod_tfrecord_api

Merge pull request !6472 from yanghaitao/yht_celeba_get_dataset_size

Merge pull request !6479 from yanghaitao/yht_bucket_batch_ci

Merge pull request !6451 from yanghaitao/yht_celeba_log

Merge pull request !6346 from yanghaitao/yht_pyfunc_timeout

Merge pull request !6221 from anzhengqi/stop-send-at-eos

Merge pull request !6113 from xiefangqi/md_unify_seed