refactor:move some common codes from orm to client

[jac0626]

• Migrated connections.py, schema.py, iterator.py, types.py, constants.py from pymilvus/orm to pymilvus/client
• Add deprecated warning while using orm
• Maintained backward compatibility via re-exports in pymilvus/orm
• Updated test imports (9 files) to use pymilvus.client
• Added test_orm_deprecation.py for backward compatibility verification

also see #3133

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[codecov]

Codecov Report

❌ Patch coverage is 49.84404% with 804 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (master@f01620e). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pymilvus/client/iterator.py	22.87%	408 Missing ⚠️
pymilvus/client/schema.py	54.90%	317 Missing ⚠️
pymilvus/client/connections.py	75.62%	49 Missing ⚠️
pymilvus/client/types.py	66.66%	22 Missing ⚠️
pymilvus/orm/__init__.py	73.33%	4 Missing ⚠️
pymilvus/client/abstract.py	57.14%	3 Missing ⚠️
pymilvus/client/async_grpc_handler.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #3138   +/-   ##
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  Coverage          ?   46.44%           
=========================================
  Files             ?       70           
  Lines             ?    14007           
  Branches          ?        0           
=========================================
  Hits              ?     6505           
  Misses            ?     7502           
  Partials          ?        0           

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