Proportion of Time Spent on Cloning is Significant during `poetry lock --no-update`

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Feature Request

Title: Proportion of Time Spent on Cloning is Significant during poetry lock --no-update

Body:

While running Poetry and cProfile locally, I noticed that a significant amount of time is spent on the cloning process, as depicted in the image below.

I made some modifications to replace the clone operation with a shallow copy, copying only necessary attributes. (I adjusted it to pass the tests by defining "necessary attributes".)

As a result, I was able to significantly reduce the time spent on the cloning operation, as can be seen in the following image. In addition, the processing time also improved significantly:

From

Resolving dependencies... (58.9s)

to

Resolving dependencies... (34.5s)

Would you be interested in this improvement? If so, I would like to create a PR right away.

environment

poetry: e8ca4b32ceeb1648eaba6bed49e8b36dcfbf0cc0
poetry-core: f09d84a4c6ad6d1117998ff9d46949e1bd819f5b -> 86a0ec388eb7581c3c3b3d0f78848aa85f434893

Start by profiling poetry lock --no-update with cProfile and confirm how much time the cloning process consumes. Review the existing clone behavior and tests to determine which attributes are necessary, then verify that the tests still pass and that dependency resolution shows a measurable improvement.