fix: return error tuple on dtype/operator mismatch in Query.where predicates

[stuartjohnpage]

Summary

• fix: return clean error tuple on dtype/operator mismatch in Results.filter/2 #12 guarded Results.filter/2 against ordering operators (>, <, >=, <=) on non-orderable columns, but the same unguarded dispatch remained in Client.apply_filter/4
• Client.apply_filter/4 now performs the same dtype check and returns {:error, "operator >= not supported on :string column 'revision'"}.
• Query.process_files/3 previously hard-matched {:ok, df} from parse_parquet_files/3; it now passes an error through.

Drive-bys

• cleaned up some aliases
• orderable_dtype?/1 abstracted out

Test plan

• mix test — 8 doctests + 110 tests pass
• New regression test: Client.parse_parquet_files/3 with revision >= 1 on a string column returns {:error, msg} where msg =~ "operator >=", msg =~ "revision", msg =~ "string"
• New positive test: id >= 2 on a numeric column through the same path still filters rows correctly
• Existing Results.filter/2 dtype tests continue to pass against the shared orderable_dtype?/1

[Copilot]

🟢 Approval recommended

The functional changes are cohesive, error propagation is handled, and new tests cover both the regression and a positive path, with only a minor docstring inconsistency noted.

Pull request overview

This PR aligns client-side Parquet row filtering with the existing Results.filter/2 behavior by guarding ordering operators (>, <, >=, <=) against non-orderable Explorer dtypes, returning a descriptive {:error, message} instead of raising, and propagating that error up through query execution.

Changes:

• Add dtype/operator validation to Client.apply_filter/4 and return an error tuple for invalid ordering comparisons.
• Propagate Client.parse_parquet_files/3 failures through Query.process_files/3 instead of hard-matching {:ok, df}.
• Extract orderable_dtype?/1 into PredicateParser and add regression/positive tests for Parquet row filtering.

File summaries

File	Description
test/delta_query/client_test.exs	Adds adapter-backed tests covering valid numeric ordering filters and invalid string ordering filters.
lib/delta_query/results.ex	Refactors aliases and switches to shared PredicateParser.orderable_dtype?/1 for ordered operator validation.
lib/delta_query/query.ex	Ensures process_files/3 passes through Client.parse_parquet_files/3 errors via with.
lib/delta_query/predicate_parser.ex	Introduces public orderable_dtype?/1 helper with docs/spec for shared dtype checks.
lib/delta_query/client.ex	Returns `{:ok, df}

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Lite

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[emmy-bishop]

Lookin good!