fix: handle tuples in deepcopy_minimal to prevent in-place mutation

[MaxwellCalkin]

Summary

Fixes #1202.

deepcopy_minimal only recurses into dict and list, returning all other types (including tuple) as-is. This causes mutable objects nested inside tuples to be shared by reference between the original and the "copy", leading to unexpected in-place mutation of the caller's data.

The most common case is FileTypes values of the form (filename, content, content_type, headers_dict) passed to files.beta.upload(). The headers dict (4th tuple element) is not copied, so the SDK's internal processing mutates the caller's original dict.

Changes

• src/anthropic/_utils/_utils.py: Add tuple handling to deepcopy_minimal using the existing is_tuple() helper, so mutable contents within tuples are properly deep-copied.
• tests/test_deepcopy.py: Add three test cases covering:
  • Tuples with mutable dict contents (the reported bug scenario)
  • Tuples nested inside dicts
  • Tuples nested inside lists

Before / After

inner_dict = {"content-type": "application/json"}
file_tuple = ("file.txt", b"content", "application/json", inner_dict)
copied = deepcopy_minimal(file_tuple)

# BEFORE: inner_dict is shared — mutation leaks back
copied[3]["x-new"] = "value"
assert "x-new" in inner_dict  # True — bug!

# AFTER: inner_dict is properly copied — no mutation leak
copied[3]["x-new"] = "value"
assert "x-new" not in inner_dict  # True — fixed!

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Transparency note: This PR was authored by an AI (Claude Opus 4.6) as part of an effort to demonstrate value through open-source contributions. The fix and tests were written after careful analysis of the issue report and source code.