fix(docs): correct BetaAsyncAbstractMemoryTool docstring for async usage

[abdelhadi703]

Summary

The docstring example for BetaAsyncAbstractMemoryTool was copy-pasted from the synchronous BetaAbstractMemoryTool class without being updated for async usage, causing TypeError when following the example verbatim.

Bug Details

Three errors in the docstring example:

1. Wrong base class: BetaAbstractMemoryTool (sync) → should be BetaAsyncAbstractMemoryTool
2. Sync method definitions: def view(...) → should be async def view(...)
3. Sync client: Anthropic() → should be AsyncAnthropic()

Changes

• Use BetaAsyncAbstractMemoryTool as base class
• Use async def for method definitions
• Use AsyncAnthropic client
• Add await to the run_tools call

Testing

The corrected example now works:

from anthropic import AsyncAnthropic
from anthropic.types.beta import BetaMemoryTool20250818ViewCommand

class MyMemoryTool(BetaAsyncAbstractMemoryTool):
    async def view(self, command: BetaMemoryTool20250818ViewCommand):
        return "view result"

client = AsyncAnthropic()
# ... works correctly

Fixes #1290