16. Start Positions and Lambdas from Chunks in the VMs

• PUSHPOS pushed the start position of a sequence, repetition or atomic expression onto the value stack ([]any), and converting an int to an interface allocates for values above 255. It now pushes a *int taken from a chunk (vmMachine.newPos); the consumers (SEQ, ATOMIC, ENDREPEAT) dereference it.
• EFUNC allocated each vmFunc; lambdas never outlive the evaluation, and they now come from a chunk too (vmMachine.newFunc).
• Effect (min of 6 interleaved runs, codepoints, Apple M3 Max): allocations per parse JSON 32k → 1.9k, CSV 41k → 1.2k, XML 47k → 19k, minilang 14k → 1.4k, for both VMs. Bytes and time are unchanged (within noise); the gain is fewer objects for the GC.
• The remaining XML allocations are text(...) results: a string converted to an interface needs a header on the heap (comparisons of two texts avoid it since change 36).