Show span annotations for each fixture in dependency chain

[MatthewMckee4]

Summary

• Each intermediate fixture in a dependency chain now gets its own sub-diagnostic with a span annotation pointing to its definition
• Replaces the previous (required by db->connection) suffix with individual annotated spans
• Makes it easy to visually trace the full path from test to failing fixture

Before:

info: Fixture `config` failed here (required by `db` -> `connection`)

After:

info: Fixture `db` requires `connection`
  --> test.py:13:5
   |
12 | @fixture
13 | def db(connection):
   |     ^^

info: Fixture `connection` requires `config`
  --> test.py:9:5
   |
 8 | @fixture
 9 | def connection(config):
   |     ^^^^^^^^^^

info: Fixture `config` failed here
 --> test.py:6:5

Test plan

• Updated snapshot for test_fixture_dependency_chain_failure with new span-annotated output
• All 641 tests pass
• Pre-commit checks pass

[codspeed-hq]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 1 untouched benchmark

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_{Comparing fixture-chain-span-annotations (9e2df4f) with main (7b00a40)}