# What does this PR do?

Converts the printf-style `%s` logging calls in the VertexAI inference
provider to the project's structured key-value logging style.

The `Block f-string logging` pre-commit hook and the repository logging
conventions require key-value arguments (`logger.info("msg",
key=value)`) rather than positional `%`-formatting. These five call
sites in `vertexai.py` and `converters.py` were still using the old
positional style.

No behavioral change: the same data is logged, just emitted through
structlog key-value fields so the messages are machine-parseable and
consistent with the rest of the codebase.

## Test Plan

No runtime behavior changes. Verified via pre-commit:

```
uv run pre-commit run --all-files
```

Relevant hooks passing on the changed files:

```
Ensure 'ogx.log' usage for logging...........................................Passed
Block f-string logging (use structlog key-value style).......................Passed
ruff format..................................................................Passed
mypy.........................................................................Passed
```

Signed-off-by: Major Hayden <major@mhtx.net>