parser: allow Map (and comma-bearing generics) as class state fields

[code-by-sia]

The state { } init-token collector tracked (), [], and {} depth but not <>, so the comma inside a generic default such as = empty Map<String, Integer> read as depth-zero and ended the field early. The result was a garbled state block; the alias workaround (type IntMap = Map<...>) then hit a second issue where empty <alias> emits a null {0} struct that crashes at first use.

Fix

Track </> (token kinds 114/115) in the collector, so a Map (or any comma-bearing generic) can be a class state field directly. Construction goes through the existing, correct empty Map<...> codegen path, so no {0} and no alias needed:

class Counter {
    state { counts: Map<String, Integer> = empty Map<String, Integer> }
    consumer add(k: String) { this.counts.put(k, this.counts.getOr(k, 0) + 1) }
}

Follow-through

The metrics Meter (std/monitoring/instruments.xi, added with the tracing suite) used a scanned List<compound> to work around this. It now uses Maps directly with O(1) lookups, dropping ~40 lines.

Verification

• New regression test examples/language/map_state_test.xi.
• Self-hosting fixpoint holds (gen2 == gen3); all 45 existing test files pass.
• Still out of scope (separate gap): Map<String, SomeCompound> (compound values) is not monomorphized; use List<compound> there.