Revert band_name model field change; remove assertion from test instead

[Copilot]

The previous commit converted FeedResult.band_name from a @property to a Pydantic model field to satisfy a type checker, but the correct fix is to remove the test assertion rather than alter the model.

Changes

• models/feed.py: Restored band_name as a computed @property returning f"f{self.frequency}"
• client/feed.py: Removed the now-unnecessary explicit band_name=f"f{frequency}" from FeedResult construction
• tests/test_backend/test_feed.py: Dropped assert feed.band_name == "f145" — the property is an implementation detail, not a contract worth asserting in integration tests

# Before: band_name promoted to a required model field
class FeedResult(BaseModel):
    frequency: int
    band_name: str  # ← added to appease type checker

# After: back to a derived property
class FeedResult(BaseModel):
    frequency: int

    @property
    def band_name(self) -> str:
        return f"f{self.frequency}"

Original prompt

Good morning! I would like you to continually run ty check lightcurvedb/storage/postgres and resolve all issues. Make minimal changes.

The user has attached the following file paths as relevant context:

• .github/copilot-instructions.md

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[JBorrow]

Now that is fixed, please apply the new pattern (i.e. with the PostgresPoolUser subclass) to the timescale/ storage dependency.