CLI: Duplicate `concurrency` argument causes the CLI to silently exit with code 0 after the synth phase

### Describe the bug

Running the `cdk deploy` command and passing multiple instances of the `--concurrency` argument causes the CLI to halt after the synth phase and exit with code `0` and no output.

This causes deployments to **silently** fail. Nothing happens after the synth phase, which means the CDK does not communicate with CloudFormation, and stacks are not deployed. When used in a CI/CD context, this can cause transparent failures: exit code 0, the CI job is marked as successful, but no software has been deployed.

I fully understand this problem can be avoided by not using the same parameter multiple times, but the lack of validation can cause unexpected behaviors.

### Expected Behavior

Either:

1. The parsed args would "ignore" the first entry of the argument and use the second entry as the final value.
2. The CLI would throw an error because of an invalid argument type.

### Current Behavior

The CLI exits with code `0` and no error output straight after the synth phase.

### Reproduction Steps

On any CDK project I've tried, run:

```
npm run cdk -- deploy --concurrency 1 --concurrency 10 --all
```

The last line of the output is:

```
✨ Synthesis time: 14.7s
```

The exit code is `0`, and nothing else happens. With `verbose` mode enabled, I inspected the parsed arguments, and I can see the `concurrency` arg is turned into an array (this is the default behavior of the `yargs` library):

```
concurrency: [ 1, 10 ],
```

### Possible Solution

#### Validation

The `yargs` library lacks proper validation for the arguments (from what I've seen), but this issue could arise with an unpredictable amount of other CLI arguments. I feel like there should be a degree of validation of the arguments directly in the AWS CDK CLI.

It could also be a per-command Joi validation done on the incoming command arguments (e.g. put the validation of a Joi schema [here](https://github.com/aws/aws-cdk/blob/3eef58928f77cf1b7a79c228446cc39be6dbd2f1/packages/aws-cdk/lib/cdk-toolkit.ts#L119)).

This specific issue could be solved by disabling the [`duplicate-arguments-array`](https://github.com/yargs/yargs-parser#duplicate-arguments-array) config option, but this would also disable the ability to specify the same parameter multiple times to populate an array, which does not sound like the right way to go.

#### Another lib?

Have you considered using [`commander.js`](https://github.com/tj/commander.js)? It has a similar approach to `yargs` but a more predictable behavior.

I ran [a simple test](https://gist.github.com/cmaster11/e61550477c44a29d14c873564023b16e) with both libraries, and `commander.js` works as I'd normally expect an args-parsing library to do.

```shell
# node index.js --str "a string" --arr "array string 1"
### yargs
args: { str: 'a string', arr: [ 'array string 1' ] }
### commander
args: { str: 'a string', arr: [ 'array string 1' ] }

# node index.js --str "a string" --arr "array string 1" --str "another string" --arr "array string 2"
### yargs
args: {
str: [ 'a string', 'another string' ],
arr: [ 'array string 1', 'array string 2' ]
}
### commander
args: {
str: 'another string',
arr: [ 'array string 1', 'array string 2' ]
}

```

### Additional Information/Context

There are some open issues about the lack of validation in the `yargs` repo:

https://github.com/yargs/yargs/issues/110
https://github.com/yargs/yargs/issues/1079

### CDK CLI Version

2.147.3 (build 32f0fdb)

### Framework Version

_No response_

### Node.js Version

Node.js v20.10.0

### OS

MacOS 14.4.1 (23E224)

### Language

TypeScript

### Language Version

TypeScript 4.9.5

Start with packages/aws-cdk/lib/cdk-toolkit.ts around the linked line 119 and trace how yargs parses duplicate options before deployment begins. Reproduce the command with two --concurrency values, then verify that invalid duplicates no longer silently stop after synthesis and that the CLI reports the problem or applies a defined final value.

Written by the indexing model from the issue text.