Built-in Map and Set collections (pipe-fence [|K => V|] / [|T|])

[assapir]

Built-in Map and Set collection types — the first slice of #72. These are built-in parametric collection primitives (like []T), not user-defined generics.

What's implemented (built-in keys only)

• Syntax — pipe fence. Map type [|K => V|], literal [|"a" => 1|], empty [|=>|]; Set type [|T|], literal [|"a", "b"|], empty [||]. The fence keeps a set literal distinct from an array literal.
• Immutable / persistent — every mutating method returns a NEW collection.
• Fail-loud access mirroring arrays — m[k] returns the value and crashes on a missing key; m.get(k) is the safe Ok(v)/NotOk form.
• Method surface — Map: get/has/set/keys/values/each + the .size field. Set: has/add/items/each + .size.
• Set algebra — + union, - difference, +- (= -+) intersection (single-token symmetric operators; whitespace disambiguates from + -, per the locked design).
• Native-backed by plain std::collections::HashMap/HashSet in quilon-rt over GC memory. Keys are the built-in hashable types (Num / Text / Bool; Text hashes by content, consistent with value ==).
• Iteration order is unspecified; a fixed-seed BuildHasher keeps programs reproducible run-to-run (order is unspecified by contract, not insertion order).
• 18 runtime intrinsics registered through the existing intrinsic_registry! macro; the intrinsic_link_test reaches every one under both linkers.

Deferred to a later slice (per #72)

• User-defined key hashing — the %/== hooks and their compile-time pairing + debug-build consistency check.
• remove.
• Handing ^'s env over as a [|Text => Text|] map (and core.cli's getEnv adaptation).

Ships with

• docs/LANGUAGE.md: Maps and Sets section, symbol-table entries, and feature-matrix rows.
• tests/collections_test.rs: run + type-error suite; a subprocess test for the fail-loud m[k] miss.
• examples/maps_and_sets.ql: a self-asserting demo (order-independent asserts only).

Notes for review

• Rebased onto current main (concurrency runtime, deferred values, docs/corelib split). Conflicts were clean unions in the intrinsic registry and codegen; new MapLit/SetLit arms were added to main's post-fork deferral.rs/reachability.rs.
• Read-only correctness + simplification review passes applied. No bugs found; cleanups (decorative comments, spelled-out identifiers) folded in.

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