fix(interp): deftype fails at its own form with a locating error - #355

…ith tests

The merge of main into upstream/deftype resolved the conflict in
interp/special.rs by keeping BOTH sides of eval_deftype: a truncated copy of
the new one — its body cut off after the field-spec parse and an orphan
fragment of intern_type_symbol's body spliced in, referencing `globals` and
`ns` that do not exist there — followed by csm#355's old "not implemented" stub.
That is E0428 plus two E0425, so cljrs-runtime did not compile at all: both the
WASM build and Build/test/lint went red, the WASM job on the compile errors and
the lint job on rustfmt drift the same merge left behind.

Three things the merges silently reverted, restored:

1. eval_deftype's body. It registers the protocol impls with the mutable field
   names, builds the positional ->T constructor (routing to
   make-type-instance-mut when the type declares mutable fields) and interns
   the type symbol. The duplicate stub is gone.

2. defrecord's field parse, back onto the shared parse_field_specs rather than
   a second hand-rolled copy. parse_field_specs now reads the vector through
   `as_vector`, so a marker on the field vector itself — (defrecord R ^:marker
   [x]) — stays transparent for deftype as it already was for defrecord.

3. resolve_protocol_sym's three call sites (PR csm#354). The merges dropped all
   three back to lookup_in_ns(current_ns, "mp/IThing"), leaving the helper dead
   — which also fails `clippy -D warnings` — and cross-namespace protocol impls
   broken again with "mp/IThing is not a protocol".

Everything outside special.rs survived and is unchanged: TypeInstance.mutable,
the serialize fold, rt_assoc, the set! lowering declines, .-field dispatch and
the make-type-instance-mut builtin.

Nothing caught any of this, because nothing tested the behaviour — so:

- deftype_types.rs: the constructor, .-field, instance?, the absent map->T,
  fields in scope in a method body, multi-protocol dispatch, set! in both forms,
  instance independence, and mixed immutable/mutable fields.
- deftype_mutable_tiered.rs: its own binary so it can force eager IR lowering
  process-wide. Three of its four tests fail when the set!-on-a-local decline
  is removed ("IR interpreter: var not found user/n"), and the immutable
  control still passes — the tree-walking tests cannot discriminate there.
- qualified_protocol_impl.rs: all five impl sites across a namespace boundary,
  by alias and fully qualified, plus the same-ns control. Six of the seven fail
  when resolve_protocol_sym is neutered.

Docs: differences.md and TODO.md said deftype is not implemented; the crate
READMEs now carry TypeInstance.mutable, the shared deftype/defrecord helpers,
the .-field dispatch rule and the set! lowering decline.

Verified: cargo fmt --check, clippy --workspace -D warnings, cargo test
--workspace, the wasm32-unknown-unknown release build, and the AOT
clojure-test-suite (310 tests / 5543 assertions, 0 failures).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wdq2umKkdALhZbbGMxM8n1