* feat: add inheritable-only field to hide processor-level targets from listing
Processor-level targets like esp32, rp2040, etc. have flash-method set
so they leak through the existing heuristic filter in GetTargetSpecs and
appear in `tinygo targets` output. Add an "inheritable-only" JSON field
that is checked on raw JSON before inheritance resolution, preventing
these non-board targets from being listed while keeping them loadable
for direct builds and inheritance.
Ref: tinygo-org/tinygo#5178
* fix: prevent inheritable-only from propagating to child targets
The InheritableOnly bool field was propagating from parent to child
targets through overrideProperties, which would hide board targets
from GetTargetSpecs. Fix by preserving/restoring the field across
resolveInherits. Also simplify GetTargetSpecs by removing the raw
JSON pre-check workaround and remove nonexistent esp32c6 from tests.
* prevent build commands to use inheritable only targets
Carlos Henrique Guardão Gandarez
soypat