Add type hash to names_and_types (#356)

[tisomi]

Description

This PR extends rmw_names_and_types_t with a type_hashes parallel array, so the
ROS graph query APIs (rmw_get_topic_names_and_types, rmw_get_service_names_and_types,
and the per-node variants) can expose the type hash of each name/type pair alongside the
existing names and types arrays. The new array is indexed in lockstep with the others:
type_hashes[i][j] corresponds to types[i].data[j].

Alongside the struct change, the lifecycle helpers were updated and hardened:

• rmw_names_and_types_init now enforces the documented zero-initialized precondition on
  its output argument, returning RMW_RET_INVALID_ARGUMENT when it is not zero-initialized.
  Previously the precondition was documented but unchecked, so passing a populated struct
  would silently leak. It also allocates and unwinds the new type_hashes array, restoring
  the struct to the zero state on any allocation failure so the caller can re-init without
  leaking.
• rmw_names_and_types_fini now cleans up the type_hashes array and finalizes partially-initialized structs — e.g. one left by a middleware
  populate that inits the full struct then fails mid-fill — freeing the new type_hashes
  array row-by-row (skipping rows still NULL) instead of leaking it. The unconditional
  names cleanup is a no-op on a zero-initialized names array.

Updated the doxygen across the affected headers to mention type hashes.

New fault-injection tests cover the type_hashes allocation-failure path and assert the
output struct is restored to the zero state after RMW_RET_BAD_ALLOC, so the caller can
re-init without leaks.

Note: this extends a public struct and is therefore an ABI break.

This is the interface half of the change; populating the field is handled in the companion
middleware PRs (see Additional Information).

Related: Issue #356

Is this user-facing behavior change?

Yes.

• rmw_names_and_types_t gains a type_hashes member — an ABI break; downstream consumers
  must be rebuilt against the new layout.
• Once paired with the middleware PRs, the graph query APIs report the type hash of each
  name/type pair.
• rmw_names_and_types_init now rejects a non-zero-initialized output argument with
  RMW_RET_INVALID_ARGUMENT. Callers that already follow the documented contract (passing a
  struct from rmw_get_zero_initialized_names_and_types()) are unaffected; callers that
  relied on the previous unchecked behavior get an explicit error instead of a silent leak.

Did you use Generative AI?

Yes. Claude (claude-sonnet-4-6) via GitHub Copilot was used to explore the codebase and
create an initial prototype.

Additional Information

• Companion PRs completing the feature:
  • rmw_dds_common #89: "Populate type hashes in graph cache names_and_types"
  • rmw_zenoh #1004: "Populate type hashes in zenoh graph cache"
• The new header include (rosidl_runtime_c/type_hash.h) needs no packaging change:
  rosidl_runtime_c is already a build/build_export dependency of this package.

Testing

• Ran the package unit tests (including the new fault-injection cases) in a Docker
  container; all pass.
• Implemented and successfully ran an integration test exercising the end-to-end
  type-hash path through the graph query APIs.

This is a SIEMENS activity and was initialized by @gramss

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