tests(commands/mcms): isolate cobra command per parallel subtest (#734)

## What changed
- Updated `TestSubcommands_HaveRequiredFlags` in
`engine/cld/commands/mcms/command_test.go` so each parallel subtest
creates its own command instance.
- Removed the shared command instance that was previously reused across
parallel subtests.

## Why
Consistently failing for test due to race condition -
https://github.com/smartcontractkit/chainlink-deployments-framework/actions/runs/22008698619/job/63598036705

```
==================
==================
WARNING: DATA RACE
Read at 0x00c000b65560 by goroutine 212:
  github.com/spf13/pflag.(*FlagSet).VisitAll()
      /home/runner/go/pkg/mod/github.com/spf13/pflag@v1.0.10/flag.go:305 +0x3a
  github.com/spf13/pflag.(*FlagSet).AddFlagSet()
      /home/runner/go/pkg/mod/github.com/spf13/pflag@v1.0.10/flag.go:915 +0x93
  github.com/spf13/cobra.(*Command).mergePersistentFlags()
      /home/runner/go/pkg/mod/github.com/spf13/cobra@v1.10.1/command.go:1900 +0x2f
  github.com/spf13/cobra.stripFlags()
      /home/runner/go/pkg/mod/github.com/spf13/cobra@v1.10.1/command.go:678 +0x64
  github.com/spf13/cobra.(*Command).Find.func1()
```
```
==================
--- FAIL: TestSubcommands_HaveRequiredFlags (0.00s)
    --- FAIL: TestSubcommands_HaveRequiredFlags/analyze-proposal (0.00s)
        testing.go:1617: race detected during execution of test
    --- FAIL: TestSubcommands_HaveRequiredFlags/execute-fork (0.00s)
        testing.go:1617: race detected during execution of test
    --- FAIL: TestSubcommands_HaveRequiredFlags/error-decode-evm (0.00s)
        testing.go:1617: race detected during execution of test
```

Author: graham-chainlink

engine/cld/commands/mcms/command_test.go

@@ -126,9 +126,6 @@ func TestNewCommand_InvalidConfigReturnsError(t *testing.T) {
 func TestSubcommands_HaveRequiredFlags(t *testing.T) {
 	t.Parallel()
 
-	cmd, err := newTestCommand(t)
-	require.NoError(t, err)
-
 	tests := []struct {
 		subcommand string
 		flags      []string
@@ -155,6 +152,9 @@ func TestSubcommands_HaveRequiredFlags(t *testing.T) {
 		t.Run(tt.subcommand, func(t *testing.T) {
 			t.Parallel()
 
+			cmd, err := newTestCommand(t)
+			require.NoError(t, err)
+
 			subCmd, _, err := cmd.Find([]string{tt.subcommand})
 			require.NoError(t, err)
 			require.Equal(t, tt.subcommand, subCmd.Use)