Migrate off deprecated `qcodes.instrument.base` module

[marcosfrenkel]

Context

Every test run surfaces this warning:

```
src/instrumentserver/blueprints.py:68: QCoDeSDeprecationWarning: The `qcodes.instrument.base` module is deprecated. Please consult the api documentation at https://microsoft.github.io/Qcodes/api/index.html for alternatives.
from qcodes.instrument.base import InstrumentBase
```

qcodes 0.55.0 has removed `InstrumentBase` from the deprecated submodule path. The canonical public import is:

```python
from qcodes.instrument import InstrumentBase
```

(The actual implementation now lives at `qcodes.instrument.instrument_base`, but consumers should use the package-level re-export, not the underscored module.)

Sites

```
src/instrumentserver/blueprints.py:68
src/instrumentserver/client/proxy.py:21
src/instrumentserver/params.py:9
src/instrumentserver/serialize.py:76
```

All four use the same `from qcodes.instrument.base import InstrumentBase` pattern.

Fix

Replace each occurrence:

```python

• from qcodes.instrument.base import InstrumentBase

• from qcodes.instrument import InstrumentBase
  ```

Verification

• `uv run pytest` no longer emits `QCoDeSDeprecationWarning` for these modules.
• `uv run mypy` and `uv run ruff check src/` remain green.
• Functional behaviour unchanged (`InstrumentBase` is the same class; only the import path differs).

Notes

While here, it's worth a quick audit of other deprecated qcodes paths surfaced by the same release. Likely candidates to check:

• `qcodes.instrument.parameter` — many parameter types now re-exported from `qcodes.parameters`.
• `qcodes.instrument.channel` — same story for `InstrumentChannel` / `ChannelList` (current code already imports `InstrumentChannel` from the top-level `qcodes`, which is fine).

Out of scope for this issue if no warnings fire from those paths in CI; in scope if they do.

Related

• PR Modernizing packaging #127 — packaging modernization (where the warning currently surfaces in CI logs).