test: read the bootstrap topology fixture from this repo

flowchart LR
  T["test_topology_bootstrap.py<br/>test_tfsdk_registry_wiring.py"] -- "before: ../tf-sdk/tests/contract/bootstrap_example.yaml" --> X["only exists with a tf-sdk checkout<br/>next to SRM (not in CI)"]
  T -- "now: tests/fixtures/tf_sdk_bootstrap_example.yaml" --> F["copied into this repo, unchanged"]

Every pipeline on refactor/tf-sdk-wiring fails test on the same 6 tests (e.g. pipeline 28530). They read their topology fixture from a tf-sdk checkout next to SRM, and CI only clones SRM. This MR copies the file into tests/fixtures/ unchanged (same content as tf-sdk's refactor/tfsdk-architecture-alignment) and points both tests at the copy.

CI job, run locally	refactor/tf-sdk-wiring (pipeline 28530)	this MR	this MR + SRM !37 (merged)
test	477 passed, 6 failed	483 passed	486 passed
type (mypy)	clean	clean	clean
architecture (lint-imports)	2 kept	2 kept	2 kept
lint, format (ruff)	clean	clean	clean

When tf-sdk's example changes, update the copy. After this merges, rebase SRM !37 (merged) so its pipeline goes green.