test: Adding 19 server/app integration tests

[mindpower]

Description

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Added 19 servers/app integration tests. The test coverage is now around 85% (from 79% previously)

________________________________________________ coverage: platform darwin, python 3.13.3-final-0 _________________________________________________

Name                                                         Stmts   Miss Branch BrPart  Cover
----------------------------------------------------------------------------------------------
src/a2a/client/client.py                                        74     26     18      4    63%
src/a2a/client/errors.py                                        10      0      0      0   100%
src/a2a/client/helpers.py                                        2      0      0      0   100%
src/a2a/server/agent_execution/agent_executor.py                 1      0      0      0   100%
src/a2a/server/agent_execution/context.py                       63     16     28      9    68%
src/a2a/server/apps/http_app.py                                  1      0      0      0   100%
src/a2a/server/apps/starlette_app.py                            80      5     24      3    92%
src/a2a/server/events/event_consumer.py                         41      6      6      2    83%
src/a2a/server/events/event_queue.py                            34      5      6      2    82%
src/a2a/server/events/in_memory_queue_manager.py                32      8     10      4    67%
src/a2a/server/events/queue_manager.py                           3      0      0      0   100%
src/a2a/server/request_handlers/default_request_handler.py     140     20     48     14    82%
src/a2a/server/request_handlers/jsonrpc_handler.py              54      8      8      2    84%
src/a2a/server/request_handlers/request_handler.py               1      0      0      0   100%
src/a2a/server/request_handlers/response_helpers.py             12      5      4      1    50%
src/a2a/server/tasks/inmemory_push_notifier.py                  27      5      4      1    74%
src/a2a/server/tasks/inmemory_task_store.py                     25      0      4      0   100%
src/a2a/server/tasks/push_notifier.py                            1      0      0      0   100%
src/a2a/server/tasks/result_aggregator.py                       38     11     16      4    69%
src/a2a/server/tasks/task_manager.py                            82      9     34      5    84%
src/a2a/server/tasks/task_store.py                               1      0      0      0   100%
src/a2a/server/tasks/task_updater.py                            19     10      0      0    47%
src/a2a/types.py                                               472      0      0      0   100%
src/a2a/utils/artifact.py                                        6      3      0      0    50%
src/a2a/utils/errors.py                                          8      0      0      0   100%
src/a2a/utils/helpers.py                                        50      5     20      1    86%
src/a2a/utils/message.py                                         8      4      0      0    50%
src/a2a/utils/task.py                                            6      4      2      0    25%
src/a2a/utils/telemetry.py                                      76      4     18      1    93%
----------------------------------------------------------------------------------------------
TOTAL                                                         1367    154    250     53    85%
======================= 148 passed, 2 warnings in 1.64s ========================