[Lane 2 · kotlin-core] NotImplemented stubs — convTranspose1d for non-FP32 dtypes on CPU #1421

Sub-issue of #1414 ([Feature]: Close the remaining NotImplemented stubs outside the operator surface).

Lane: 2 · Kotlin core
Skill needed: Kotlin; CPU kernels.
Size: s (a few hours)
Blocked by: nothing

What to do

1. DefaultCpuOps.convTranspose1d casts every element as Float, so it only works for FP32.
2. Dispatch on dtype the way conv1d does, with tests for FP16 and Int8 (or document and reject unsupported dtypes explicitly).
3. Run ./gradlew :skainet-backends:skainet-backend-cpu:jvmTest.

Acceptance

• Non-FP32 inputs either compute correctly or fail with a clear dtype error
• Result reported back on the parent issue

Notes

If something here turns out to be wrong or much bigger than the size label, comment on this issue or open a specific bug instead of blocking the parent.

Coverage matrix: docs/modules/ROOT/pages/reference/ops-status-matrix.adoc · How lanes work: Issue taxonomy