Migrating pure collection method names

Harn collection methods return new values and never modify their receivers. Their names now make that value semantics explicit:

Legacy spelling	Canonical replacement
list.push(value)	list.appending(value)
list.pop()	list.dropping_last()
list.sort()	list.sorted()
list.sort_by(key)	list.sorted_by(key)
list.reverse()	list.reversed()
string.reverse()	string.reversed()
set.add(value)	set.adding(value)
set.remove(value) / set.delete(value)	set.removing(value)
dict.merge(other)	dict.merging(other)
dict.remove(key)	dict.removing(key)
dict.rekey(fn)	dict.rekeyed(fn)

Only the names changed. Return values, ordering, copy-on-write behavior, and error behavior are unchanged. In particular, dropping_last() returns a list without its last item; use last() to read the last item.

The legacy spellings remain behavior-compatible aliases so existing scripts can upgrade without a flag day. New code should use the canonical spellings. Replace legacy collection method calls, then run:

harn check .
harn lint .
harn fmt --check .

Apply replacements to collection receivers, not unrelated APIs or user methods. Calls such as git.push(...), stream.merge(...), storage delete(...), and a user-defined add(...) retain their existing names.