Emit input_json events for server tool use streams

[pragnyanramtha]

Summary

• emit input_json stream events for server tool use blocks by reusing the existing TRACKS_TOOL_INPUT aliases
• keep normal tool use and beta MCP tool use behavior unchanged
• add normal and beta regression coverage for server tool use input_json_delta events

Validation

• pytest tests/lib/streaming/test_messages.py tests/lib/streaming/test_beta_messages.py tests/lib/streaming/test_partial_json.py
• ruff check src/anthropic/lib/streaming/_messages.py src/anthropic/lib/streaming/_beta_messages.py tests/lib/streaming/test_messages.py tests/lib/streaming/test_beta_messages.py
• ruff format --check src/anthropic/lib/streaming/_messages.py src/anthropic/lib/streaming/_beta_messages.py tests/lib/streaming/test_messages.py tests/lib/streaming/test_beta_messages.py
• pyright src/anthropic/lib/streaming/_messages.py src/anthropic/lib/streaming/_beta_messages.py tests/lib/streaming/test_messages.py tests/lib/streaming/test_beta_messages.py
• mypy src/anthropic/lib/streaming/_messages.py src/anthropic/lib/streaming/_beta_messages.py
• git diff --check

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