feat: add array helpers

[knoal]

Summary

• add a minimal aiken/array module
• expose safe construction and indexing helpers
• add a bounded read-only traversal layer on top of CIP-138 arrays

Current API

from_list : List<a> -> Array<a>
length : Array<a> -> Int
is_empty : Array<a> -> Bool
at : Array<a> -> Int -> Option<a>
foldl : Array<a> -> b -> fn(a, b) -> b
foldr : Array<a> -> b -> fn(a, b) -> b
to_list : Array<a> -> List<a>
map : Array<a> -> fn(a) -> result -> Array<result>
all : Array<a> -> fn(a) -> Bool -> Bool
any : Array<a> -> fn(a) -> Bool -> Bool

Slice-4 scope

This extends the initial wrapper layer into a read-only array ergonomics core:

• traversal/composition helpers only
• no broader pull-array collection redesign yet
• no syntax/literal work
• no mutating semantics

Notes

• This PR depends on compiler-side CIP-138 array support in aiken-lang/aiken
• Companion compiler PR: feat: add CIP-138 array builtin support aiken#1353
• Kept as draft because the stdlib surface depends on unreleased compiler support

Validation

• module-focused check:
  • /home/alex/.openclaw/workspace/tmp/wt-1256/target/release/aiken check /home/alex/.openclaw/workspace/tmp/stdlib-1256 -m aiken/array
• full stdlib check:
  • /home/alex/.openclaw/workspace/tmp/wt-1256/target/release/aiken check -S /home/alex/.openclaw/workspace/tmp/stdlib-1256

Commit progression

• e6c4b0d — feat: add array helpers
• 4cd08cf — feat: add array traversal helpers