(events): Match.cidr rejects IPv6 addresses with an embedded IPv4 address

### Describe the bug

`events.Match.cidr()` throws `Invalid IP address range` at synth time for any IPv6 range that embeds an IPv4 address, and accepts a malformed one.

### Regression?

No

### Last known working version

n/a

### Expected Behavior

`Match.cidr('::ffff:192.168.0.1')` and `Match.cidr('64:ff9b::192.0.2.33/96')` should be accepted — both are valid CIDR ranges (RFC 4291 §2.5.5 IPv4-mapped, RFC 6052 NAT64). `Match.cidr('::ffff:1dd.1dd.1dd.1dd')` should be rejected.

### Current Behavior

```
Error: Invalid IP address range: ::ffff:192.168.0.1
Error: Invalid IP address range: 64:ff9b::192.0.2.33/96
```

and `::ffff:1dd.1dd.1dd.1dd` is accepted.

### Reproduction Steps

```ts
import { Match } from 'aws-cdk-lib/aws-events';

Match.cidr('2001:db8::/32'); // ok
Match.cidr('::ffff:192.168.0.1'); // throws
```

### Possible Solution

The IPv6 regex in `aws-events/lib/event-pattern.ts` lost its backslashes in the embedded-IPv4 alternatives — `(25[0-5]|2[0-4]d|1dd|[1-9]?d)` matches the literal letter `d` rather than `\d`, and the `.` separator matches any character. Restoring `\d`, `\.` and `\s` fixes it.

### Additional Information/Context

The same regex is duplicated in `aws-ec2/lib/prefix-list.ts` and has the same defect.

### CDK CLI Version

n/a (synth-time validation)

### Framework Version

aws-cdk-lib (current main)

### Node.js Version

20.x

### OS

macOS

### Language

TypeScript

Start at events.Match.cidr() and inspect the IPv6 validation regex in aws-events/lib/event-pattern.ts, then compare the duplicated regex in aws-ec2/lib/prefix-list.ts. Verify the stated IPv4-embedded IPv6 examples: valid addresses should be accepted and the malformed address should be rejected.

Written by the indexing model from the issue text.