tf.nest package when we dev theese code , flatten and map_structure pack_sequence_as are need eagerly

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System information

• Have I written custom code (as opposed to using a stock example script provided in TensorFlow):
• OS Platform and Distribution (e.g., Linux Ubuntu 16.04 x86_64):
• TensorFlow installed from (source or binary):
• TensorFlow version (use command below):
• Java version (i.e., the output of java -version):
• Java command line flags (e.g., GC parameters):
• Python version (if transferring a model trained in Python):
• Bazel version (if compiling from source):
• GCC/Compiler version (if compiling from source):
• CUDA/cuDNN version:
• GPU model and memory:

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Code to reproduce the issue
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首先定位 tf.nest 包及其 flatten、map_structure 和 pack_sequence_as 实现。该 issue 未提供复现、预期行为、文件路径或测试，因此首先确定“eagerly”对这些 API 的含义，并在定义完成检查之前识别现有覆盖范围。