lang F1 4.2: parameterized protocol as a runtime value type

VL(s64) used as a value/field type resolved to a 0-field stub (size 0); a
plain protocol was already a 16-byte {ctx,vtable} value. New
instantiateParamProtocol materializes a parameterized protocol per
instantiation: a 16-byte protocol value (is_protocol), protocol_decl_map
methods resolved under the type-arg binding (get -> T becomes get -> s64 for
VL(s64)), a vtable struct, and the type-arg binding recorded for projection.
Hooked into resolveParameterizedWithBindings before the empty-struct fallback.

xx-erasing a conforming struct into VL(s64)/VL(string) + method dispatch now
works (examples/206). This is the keystone for the canonical Combined field
(..VL(Ts)). 241 examples + unit green.

tests/expected/206-parameterized-protocol-value.exit

@@ -0,0 +1 @@
+0

tests/expected/206-parameterized-protocol-value.txt

@@ -0,0 +1,2 @@
+a.get=42
+b.get=hi