[nikhilchowdary]

Add x-goog-is-transaction routing header in python SDK to differentiate transactional requests and non-transactional requests from each other. Having a routing header for transactions helps in routing grpc requests at GFE.

This commit attaches the x-goog-is-transaction routing header to all RPCs

• Set to true for transactional RPCs
  -- beginTransaction
  -- rollback
  -- transactional commit
  -- transactional lookup
  -- transactional runQuery
  -- transactional runAggregationQuery.

• Set to false for non transactional RPCs
  -- allocateIds
  -- non transactional commit
  -- non transactional lookup
  -- non transactional runQuery
  -- non transactional runAggregationQuery.

cc: @MarkDuckworth

[gemini-code-assist]

Code Review

This pull request introduces transaction metadata tracking across Google Cloud Datastore client requests by adding a 'metadata' parameter to propagate the 'x-goog-is-transaction' header. This header is set dynamically depending on whether the request is transactional or non-transactional. Feedback on these changes includes a recommendation to use 'headers.update(metadata)' instead of a 'for' loop to avoid potential 'ValueError' exceptions when 'metadata' is a dictionary, as well as a suggestion to format multi-line function calls in accordance with PEP 8.

[gemini-code-assist]

Using a for k, v in metadata loop to unpack metadata will raise a ValueError if metadata is passed as a dictionary (since iterating over a dict yields only its keys).

Using headers.update(metadata) is more robust and idiomatic, as dict.update() natively supports both dictionaries and iterables of key-value pairs (like tuples of tuples).

    if metadata:
        headers.update(metadata)

[gemini-code-assist]

To adhere to PEP 8 style guidelines for multi-line function calls, each argument should be on its own line, and the closing parenthesis should be aligned with the start of the statement.

Suggested change

	timeout=timeout, metadata=metadata)
	timeout=timeout,
	metadata=metadata,
	)