feat: change chain default key to node_idx_parallel_idx style

[kuhahalong]

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feat: A new feature

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change chain default key to "node_idx_parallel_idx" style, for example:
chain key is: node_idx => eg: node_0 => represent the first node of the chain (idx start from 0)
if has parallel: node_idx_parallel_idx => eg: node_0_parallel_1 => represent the first node of the chain, and is a parallel node, and the second node of the parallel
if has branch: node_idx_branch_key => eg: node_1_branch_customkey => represent the second node of the chain, and is a branch node, and the 'customkey' is the key of the branch

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📊 Coverage Report:

File coverage threshold (20%) satisfied:	PASS
Package coverage threshold (30%) satisfied:	PASS
Total coverage threshold (75%) satisfied:	PASS
Total test coverage: 82.6% (2957/3578)

[BytePender]

LGTM