build(rust): pin toolchain to 1.96.0 + fix the two 1.96-only clippy lints (#87)

## What & why

Root-causes the recurring **Build Check** skew rather than just papering
over it again.

CI installs floating `stable` (currently **1.96**) via
`dtolnay/rust-toolchain@stable`. Local dev had drifted to an older
`stable` (**1.94**) whose clippy couldn't see two `collapsible_match`
lints that 1.96 flags — so #85's clippy pass (run on 1.94) still left
`main` red on Build Check. This is the second time a local/CI clippy
version gap has bitten the lint gate.

## Changes

- **`rust-toolchain.toml`** — pins `channel = "1.96.0"` (+ `clippy`,
`rustfmt`) so `cargo` uses the **same** toolchain locally and in CI. No
more silent skew; the toolchain is now bumped *deliberately* (edit the
file + re-run lints) instead of drifting under the gate.
- **Two `collapsible_match` fixes** (via `clippy --fix` → match guards,
behaviour-preserving):
  - `src/lsp/handlers/definition.rs` — `TypeDef` goto-definition arm
  - `src/vm/optimizer.rs` — `JumpIfFalse`/`JumpIfTrue` nop-removal arm

## Verification (with the pinned 1.96.0)

| gate | result |
|------|--------|
| `cargo clippy -- -D warnings` | ✅ exit 0 |
| `cargo fmt --check` | ✅ clean |
| `cargo test --lib` | ✅ 173/173 |

Installed `1.96.0` locally to verify against the exact toolchain CI uses
— my previous 1.94 was blind to these lints.

## Note on CI honoring the pin

CI's `dtolnay/rust-toolchain@stable` currently resolves to `1.96.0`, so
Build Check is green either way today. `rustup` honors
`rust-toolchain.toml` for `cargo` invocations, so the pin takes effect
for local dev immediately. If a future `stable` bump should *not*
override the pin in CI, the Build Check / e2e workflows can be switched
from `@stable` to the pinned version — happy to do that as a follow-up
if wanted (kept out of here to avoid touching SHA-pinned CI actions in a
lint fix).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_013wg3Mtq2QFhYi4XVw1Z6z7

---
_Generated by [Claude
Code](https://claude.ai/code/session_013wg3Mtq2QFhYi4XVw1Z6z7)_

Co-authored-by: Claude <noreply@anthropic.com>

Author: hyperpolymath

rust-toolchain.toml

@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: MPL-2.0
+# Pin the Rust toolchain so local builds and CI use the SAME compiler + clippy.
+#
+# Why this exists: CI installs `stable` (dtolnay/rust-toolchain@stable in
+# .github/workflows/security.yml + e2e.yml). When a developer's local `stable`
+# lagged CI's, clippy versions diverged (1.94 local vs 1.96 CI) and the
+# `Build Check` gate (`cargo clippy -- -D warnings`) failed on `main` with
+# `collapsible_match` lints that local clippy could not see. Pinning a single
+# version makes `cargo clippy` / `cargo fmt` deterministic across local and CI.
+#
+# Bump this deliberately (and re-run `cargo clippy` + `cargo fmt` locally)
+# rather than letting `stable` drift underneath the lint gate.
+[toolchain]
+channel = "1.96.0"
+components = ["clippy", "rustfmt"]

src/lsp/handlers/definition.rs

@@ -63,14 +63,12 @@ pub async fn goto_definition(
                     })));
                 }
             }
-            TopLevelItem::TypeDef(type_def) => {
-                if type_def.name == word {
-                    let range = span_to_range(&type_def.span, &doc.source);
-                    return Ok(Some(GotoDefinitionResponse::Scalar(Location {
-                        uri: uri.clone(),
-                        range,
-                    })));
-                }
+            TopLevelItem::TypeDef(type_def) if type_def.name == word => {
+                let range = span_to_range(&type_def.span, &doc.source);
+                return Ok(Some(GotoDefinitionResponse::Scalar(Location {
+                    uri: uri.clone(),
+                    range,
+                })));
             }
             _ => {}
         }

src/vm/optimizer.rs

@@ -282,10 +282,10 @@ impl Optimizer {
                         *target = new_indices[*target];
                     }
                 }
-                OpCode::JumpIfFalse(ref mut target) | OpCode::JumpIfTrue(ref mut target) => {
-                    if *target < new_indices.len() {
-                        *target = new_indices[*target];
-                    }
+                OpCode::JumpIfFalse(ref mut target) | OpCode::JumpIfTrue(ref mut target)
+                    if *target < new_indices.len() =>
+                {
+                    *target = new_indices[*target];
                 }
                 _ => {}
             }