Move dormant_capable? from Parser to cycle classes

[rymiwe]

Summary

Addresses jdowd's feedback from #69:

"I don't love that the dormant-capability is only revealed in Parser, but we should have a single pattern for this"

Each cycle class now declares its own dormant capability alongside recurring?:

def self.recurring? = true
def self.dormant_capable? = true   # EndOf, Within

Parser.dormant_capable_kinds now derives the list from the cycle classes instead of a hardcoded array. Adding a new dormant-capable cycle kind only requires declaring dormant_capable? on the class — no separate Parser edit needed.

Before

To make a cycle dormant-capable, you had to:

1. Add behavior to the cycle class
2. Also add its notation letter to Parser.dormant_capable_kinds = %w[E W]

After

Just declare it on the class:

def self.dormant_capable? = true

Test plan

• All 179 existing specs pass (no new specs needed — pure refactor)
• StandardRB clean

No behavior change — this is a mechanical refactor that makes cycle classes self-describing.