Add documentation and tests for fsspec PR #1944 callable set_size() support

[Copilot]

fsspec PR #1944 enables Callback.set_size() to accept callables, allowing filesystem implementations with size() methods (e.g., HadoopFileSystem) to work seamlessly. This PR provides the missing documentation and test coverage.

Changes

Enhanced Documentation (callbacks.py)

• Expanded set_size() docstring with detailed parameter descriptions for both int and callable types
• Added usage examples and behavioral notes for when callables are provided
• Documented the primary use case: filesystem objects with size() methods vs attributes

Test Coverage (test_callbacks.py)

• Added test_set_size_with_callable() covering:
  • Integer values (backward compatibility)
  • Lambda functions
  • Function references
  • Method references (primary use case)

Integration Artifacts

• Git patch files for easy application to the PR branch
• Application guide with multiple integration methods
• Background documentation explaining the problem and solution

Example Usage

from fsspec.callbacks import Callback

callback = Callback()

# Before: Only worked with integers
callback.set_size(1000)

# After: Also accepts callables
callback.set_size(lambda: 1000)
callback.set_size(filesystem_obj.size)  # Method that returns size

Files

All artifacts located in fsspec-pr-1944/:

• callbacks.py, test_callbacks.py - Updated implementation files
• *.patch - Git patches for application to fsspec repository
• Documentation suite (README, guides, summaries)

Original prompt

针对该 pr fsspec/filesystem_spec#1944

请完善对应的 doc 并查看是否有该文件对应的测试用例，如果有的话请添加一个测试用例

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