apl: inline assignment a ← rhs mid-expression (+5 tests)

Parser: :name clause now detects 'name ← rhs' patterns inside
expressions. When seen, consumes the remaining tokens as RHS,
parses recursively, and emits a (:assign-expr name parsed-rhs)
value segment.

Eval-ast :dyad and :monad: when the right operand is an
:assign-expr node, capture the binding into env before
evaluating the left operand.  This realises the primes idiom:

  apl-run "(2 = +⌿ 0 = a ∘.| a) / a ← ⍳ 30"
  → 2 3 5 7 11 13 17 19 23 29

Also: top-level x←5 now evaluates to scalar 5 (apl-eval-ast
:assign just unwraps to its RHS value).

Caveat: ⍵-rebinding (the original primes.apl uses
'⍵←⍳⍵') is a :glyph-token; only :name-tokens are handled.
A regular variable name (like 'a') works.

lib/apl/tests/pipeline.sx

@@ -337,3 +337,25 @@
   "compress: filter even values"
   (mkrv (apl-run "(0 = 2 | 1 2 3 4 5 6) / 1 2 3 4 5 6"))
   (list 2 4 6))
+
+(apl-test "inline-assign: x ← 5" (mkrv (apl-run "x ← 5")) (list 5))
+
+(apl-test
+  "inline-assign: (2×x) + x←10 → 30"
+  (mkrv (apl-run "(2 × x) + x ← 10"))
+  (list 30))
+
+(apl-test
+  "inline-assign primes one-liner: (2=+⌿0=a∘.|a)/a←⍳30"
+  (mkrv (apl-run "(2 = +⌿ 0 = a ∘.| a) / a ← ⍳ 30"))
+  (list 2 3 5 7 11 13 17 19 23 29))
+
+(apl-test
+  "inline-assign: x is reusable — x + x ← 7 → 14"
+  (mkrv (apl-run "x + x ← 7"))
+  (list 14))
+
+(apl-test
+  "inline-assign in dfn: f ← {x + x ← ⍵} ⋄ f 8 → 16"
+  (mkrv (apl-run "f ← {x + x ← ⍵} ⋄ f 8"))
+  (list 16))