fix(spanner): preserve query immutability and optimize trace config handling

[olavloite]

• Avoid spreading string queries into traceConfig, preventing span attribute pollution and correctly setting db.statement for string queries.
• Extract getQueryTraceConfig helper to eliminate duplicated trace configuration logic and guarantee null safety.
• Replace delete operations with rest destructuring across Snapshot, Dml, and BatchTransaction to preserve caller query immutability and prevent property loss on stream retries.
• Eliminate redundant intermediate shallow copies in Snapshot.prototype.runStream.
• Hoist SPANNER_ENABLE_UUID_AS_UNTYPED lookup in Snapshot.encodeParams and propagate it to codec.getType to avoid repeated process.env checks on parameter serialization.
• Reset mock stream handlers in test/transaction.ts to eliminate MaxListenersExceededWarning.

[gemini-code-assist]

Code Review

This pull request refactors the Spanner client to avoid mutating user-provided query and option objects by replacing delete operations with object destructuring. It also introduces getQueryTraceConfig to prevent spreading query objects into trace configurations, which previously caused numeric attributes to appear on spans when queries were strings. However, two critical issues were identified in the review: first, in transaction.ts, the refactored runStream method fails to merge the encoded params and paramTypes into reqOpts, which will break parameterized queries; second, in batch-transaction.ts, destructuring query directly when it is a string will lead to string-spreading bugs, and request should be destructured instead.

[olavloite]

/gemini review

[gemini-code-assist]

Code Review

This pull request refactors the Spanner client to prevent the mutation of original query and request objects by replacing property deletions with rest destructuring. It also introduces a helper function getQueryTraceConfig to safely extract SQL statements and request tags for tracing, resolving an issue where string queries were spread into trace spans as numeric attributes. However, the reviewer identified two critical issues in transaction.ts where the destructuring refactoring missed omitting client-side options like gaxOptions, json, and jsonOptions. These properties will now be incorrectly sent to the Spanner gRPC API, which could lead to validation failures or runtime errors.

[olavloite]

The lint failures are unrelated to this change.