[Feature] Better support long messages in IRC

The Goal / Use Case

PicoClaw to understand that long messages sent over IRCv3 should be treated as a single, cohesive message.

IRC is limited to 512 bytes by default and newlines indicate a new message. If a message is over 512 bytes, it is automatically split by IRC clients. PicoClaw is currently treating these as separate messages.

Proposed Solution

With batch and its multiline extension, PicoClaw will be able to take long messages as whole, singular messages instead of separately.

Potential Implementation (Optional)

Not implementing, but most of the relevant handling logic is held here:

https://github.com/sipeed/picoclaw/blob/e14f8daecbefa332b96a180a2094950b602c466f/pkg/channels/irc/handler.go#L33-L117

Impact & Roadmap Alignment

• This is a Core Feature
• This is a Nice-to-Have / Enhancement
• This aligns with the current Roadmap

Alternatives Considered

None - this is the only way to do this in IRC.