Adds grpc.Trailer parameters to TestGetSetGetSessionOptions and
TestSetRemoveSessionOptions to ensure session cookies are fully
processed before subsequent operations.

This fixes race conditions where GetSessionOptions would execute
before SetSessionOptions trailers were processed, causing the
test to read stale session state.

Fixes macOS CI failures in PR apache#626.

Adds a 50ms delay after sending cookie deletion to allow client
middleware time to process the MaxAge=-1 cookie before the next
request validates that cookies are empty.

This fixes a race condition where the validation request would
start before cookie deletion completed, causing test to fail with
'expected map[], got map[foo:baz]' on Windows CI.

Fixes Windows CI failure in PR apache#626.

…estStatelessServerSessionCookies

- TestCookiesClone: Add 50ms delay after setting cookies before validation
  to allow client middleware time to process Set-Cookie headers
- TestStatelessServerSessionCookies: Reinitialize trailer metadata before
  each RPC call to avoid stale metadata issues

These fixes address race conditions where:
1. Cookie middleware's HeadersReceived processes headers asynchronously
2. gRPC trailer metadata can contain stale values if reused across calls

Fixes ARM64 and macOS CI failures in PR apache#629.