[Feature] Support data_parser in kv_batch_get_by_meta #194

Background

#191 added data_parser / parser_args to kv_batch_get and async_kv_batch_get. The _by_meta variants were left out of that PR.

Problem

kv_batch_put returns a KVBatchMeta, and kv_batch_get_by_meta is the natural way to read those samples back, but it does not accept a parser:

meta = tq.kv_batch_put(keys=keys, partition_id="train", fields=fields)
data = tq.kv_batch_get_by_meta(meta, select_fields="input_ids", data_parser=trim, parser_args=lengths)
# TypeError: kv_batch_get_by_meta() got an unexpected keyword argument 'data_parser'

Callers have to unpack the meta and call kv_batch_get(keys=meta.keys, partition_id=meta.partition_id, ...) instead.

Proposal

• Add data_parser and parser_args to kv_batch_get_by_meta and async_kv_batch_get_by_meta, with the same contract as kv_batch_get; parser_args is aligned with meta.keys.
• Forward both to async_kv_batch_get, which the _by_meta variants already call and which already handles the parser, including the parser_args checks.
• Cover the _by_meta path in the existing e2e test for the get-side data_parser.

Related PR: #191