Delete the tree-walk interpreter (~16k LOC) and collapse the CI mode matrix

[frostney]

Summary

Delete the tree-walk interpreter (~16k LOC across 8 units) and collapse the CI mode matrix to bytecode-only.

Why

Once eval (#872), shims (#873), and the value-unit call paths (#874) are off the evaluator, the interpreter is dead weight: ~16k LOC dominated by the 12k-line Goccia.Evaluator.pas, plus the generator-continuation, pattern-matching, and comparison/assignment/type-op evaluator units and TGocciaInterpreterExecutor.

Current behavior

Two execution modes are maintained in parallel; CI runs the suite + benchmarks in both interpreted and bytecode.

Expected behavior

• The 8 interpreter-only units and the emInterpreted mode are removed (optionally a deprecated alias kept).
• The CI interpreted/bytecode matrix collapses to bytecode-only; the paired Pascal parity tests lose their interpreter half.

Scope notes

• Final step; depends on Flip all entry-point defaults to bytecode and prove parity #871/Port eval() / direct-eval to compile-to-bytecode (sever VM -> evaluator dependency) #872/Move bootstrap shims off the interpreter #873/Extract interpreter call-paths from FunctionValue / GeneratorValue #874. Parent Remove the tree-walk interpreter #825.