Reject unknown or unsupported component sections instead of silently skipping them

[JairusSW]

Problem

decodeComponent's default section branch records any unrecognized section ID in RawSections and advances past it. ErrInvalidSectionID is defined but never used.

Relevant code: https://github.com/wago-org/component-model/blob/8a61139958e559a0ae61c3f49f6e9f33fddb6a95/internal/binary/decoder.go

For an execution engine, silently skipping an unknown or unsupported definition section is unsafe. Component sections contribute definitions to ordered index spaces and may carry required validation/instantiation semantics. Continuing as though the section were absent can shift every subsequent index or omit behavior while still returning a Component that the instantiator treats as decoded.

This also affects known-but-unimplemented format additions. For example, the current Component Model grammar includes a section-12 value definition behind a gated feature; a 0.2-only engine should reject it explicitly rather than skip it and attempt to instantiate the remaining component.

Impact

Malformed or unsupported components may pass decoding and reach compilation/instantiation with a structurally incomplete model. Depending on following aliases/canons/exports, this can produce misleading out-of-range failures, bind indices to the wrong definitions, or execute a component after silently discarding required semantics.

The engine claims compatibility with a pinned Component Model feature set, so fail-open forward compatibility is the wrong boundary here.

Suggested fix

• Return ErrInvalidSectionID for IDs not present in the pinned format.
• For a known section whose feature is not implemented, return a distinct unsupported component feature/section validation error.
• Do not put semantic definition sections into RawSections; reserve raw skipping for custom section 0 only.
• Add an explicit feature/version table so future format additions cannot become implicitly accepted through the default branch.

Regression tests

• An arbitrary invalid ID such as 0xff must fail decode.
• A syntactically valid but unsupported known section must fail with an unsupported-feature error.
• A component placing aliases/exports after the skipped section must never reach instantiation.
• Custom sections must continue to be accepted and skipped with strict size bounds.