bug: intermittent error in reset/shutdown during E2E test

### What happened?

Noticed panic in stop code when debugging a test failure.

Build: https://github.com/hyperledger/firefly/actions/runs/13591410372/job/37998345407?pr=1647
Artifact download URL: https://github.com/hyperledger/firefly/actions/runs/13591410372/artifacts/2671414723

```
firefly_e2e_firefly_core_0 | panic: runtime error: invalid memory address or nil pointer dereference
firefly_e2e_firefly_core_0 | [signal SIGSEGV: segmentation violation code=0x1 addr=0x28 pc=0xd948e0]
firefly_e2e_firefly_core_0 |
firefly_e2e_firefly_core_0 | goroutine 1 [running]:
firefly_e2e_firefly_core_0 | github.com/hyperledger/firefly/internal/namespace.(*namespaceManager).WaitStop(0xc000a07b20)
firefly_e2e_firefly_core_0 | /firefly/internal/namespace/manager.go:432 +0x240
firefly_e2e_firefly_core_0 | github.com/hyperledger/firefly/cmd.run()
firefly_e2e_firefly_core_0 | /firefly/cmd/firefly.go:165 +0x80f
firefly_e2e_firefly_core_0 | github.com/hyperledger/firefly/cmd.init.func2(0xc00026af00?, {0x10b8707?, 0x4?, 0x10b8533?})
firefly_e2e_firefly_core_0 | /firefly/cmd/firefly.go:53 +0xf
firefly_e2e_firefly_core_0 | github.com/spf13/cobra.(*Command).execute(0x19977e0, {0xc0001a8040, 0x0, 0x0})
firefly_e2e_firefly_core_0 | /go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:983 +0xaca
firefly_e2e_firefly_core_0 | github.com/spf13/cobra.(*Command).ExecuteC(0x19977e0)
firefly_e2e_firefly_core_0 | /go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:1115 +0x3ff
firefly_e2e_firefly_core_0 | github.com/spf13/cobra.(*Command).Execute(...)
firefly_e2e_firefly_core_0 | /go/pkg/mod/github.com/spf13/cobra@v1.8.0/command.go:1039
firefly_e2e_firefly_core_0 | github.com/hyperledger/firefly/cmd.Execute(...)
firefly_e2e_firefly_core_0 | /firefly/cmd/firefly.go:104
firefly_e2e_firefly_core_0 | main.main()
firefly_e2e_firefly_core_0 | /firefly/main.go:27 +0x1a
````

### What did you expect to happen?

Clean stop

### How can we reproduce it (as minimally and precisely as possible)?

See build

### Anything else we need to know?

_No response_

### OS version

```console
# On Linux:
$ cat /etc/os-release
# paste output here
$ uname -a
# paste output here

# On Windows:
C:\> wmic os get Caption, Version, BuildNumber, OSArchitecture
# paste output here
```