Fix unit_labels override writing to raw_limits in TxtLoader

[jepegit]

What

TxtLoader.parse_loader_parameters had a copy-paste slip in its override handling: the unit_labels= branch updated config_params.raw_limits instead of config_params.unit_labels.

if unit_labels := kwargs.get("unit_labels", None):
    logging.critical(f"overriding unit_labels: {unit_labels}")
-   self.config_params.raw_limits.update(unit_labels)
+   self.config_params.unit_labels.update(unit_labels)

Why

• Passing unit_labels= to a loader had no effect on unit labels, so vendor column-name templates (e.g. neware's Current({{ current }})) could not be overridden this way.
• The unit-label strings silently polluted raw_limits instead.

The bug is bracketed by a correct raw_units branch above and a correct raw_limits branch immediately below, which is what makes it a copy-paste slip rather than intent. git blame traces it to a9de15c4 — "implement renaming original headers based on unit labels" — whose stated purpose was to wire unit_labels.

Test

Adds test_unit_labels_override_lands_in_unit_labels_not_raw_limits in tests/test_loader_two_stage.py: passes unit_labels={"current": "A"} to a neware loader and asserts it lands in config_params.unit_labels while raw_limits is unchanged. Verified it fails on the pre-fix code and passes after; the surrounding two-stage and port-parity suites stay green.

Notes for reviewer

Found while porting loader post-processors for #560 (PR #601); kept out of that PR to keep it scoped to the port.

🤖 Generated with Claude Code

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