Add grpc headers and deadline to unary/unary calls

[wild-endeavor]

Why are the changes needed?

FlyteRemote.wait() polls execution state by repeatedly calling sync_execution(). When one of the underlying unary gRPC calls blocks on a stale or unhealthy connection, the wait loop can appear to hang because the loop timeout cannot be evaluated until the RPC returns.

The client also did not set gRPC keepalive options explicitly, so idle TCP connection drops through load balancers or NAT could leave the next RPC waiting on a connection that should have been detected as unhealthy.

What changes were proposed in this pull request?

• Add default gRPC keepalive options to RawSynchronousFlyteClient so the client can detect dead idle connections and reconnect.
• Add a unary-unary-only scoped deadline interceptor for gRPC calls.
• Apply a default 60 second per-RPC deadline while FlyteRemote.sync_execution() is running.
• Keep streaming RPCs unaffected by the deadline interceptor.
• Map gRPC DEADLINE_EXCEEDED to FlyteTimeout and avoid retrying deadline-expired calls.
• Add unit coverage for the keepalive options, deadline interceptor behavior, channel wrapping, and sync_execution deadline scoping.

How was this patch tested?

Targeted unit tests:

/Users/ytong/envs/flytekit/bin/python -m pytest \
  tests/flytekit/unit/clients/test_raw.py \
  tests/flytekit/unit/clients/test_auth_helper.py::test_wrap_exceptions_channel \
  tests/flytekit/unit/clients/test_deadline_interceptor.py \
  tests/flytekit/unit/remote/test_remote.py::test_remote_fetch_execution \
  tests/flytekit/unit/remote/test_remote.py::test_sync_execution_sets_default_rpc_deadline \
  tests/flytekit/unit/remote/test_remote.py::test_sync_execution_accepts_rpc_deadline_override \
  tests/flytekit/unit/remote/test_remote.py::test_sync_execution_does_not_override_active_rpc_deadline \
  -q

Result: 14 passed.

A broader local run of tests/flytekit/unit/clients/test_auth_helper.py hit unrelated macOS keyring failures in the existing PKCE/deviceflow tests, so only the changed auth-helper test was included in the targeted verification above.

Setup process

No special setup beyond the existing flytekit development environment.

Screenshots

Not applicable.

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

None.

Docs link

Not applicable.