feat: centralised concept query filtering API

[gkennos]

Problem

omop-emb and omop-graph each independently implement near-identical filtering classes for Concept table queries (filtering by domain, vocabulary, concept ID, and standardisation status). This duplication creates a maintenance burden and means any
improvements need to be made in multiple places.

• omop-emb: EmbeddingConceptFilter
• omop-graph: SearchConstraintConcept

Proposed solution

Add a shared ConceptFilter implementation to omop_alchemy.cdm.query:

from omop_alchemy.cdm.query import ConceptFilter

f = ConceptFilter(
    domains=("Condition", "Drug"),
    require_standard=True,
)
filtered_query = f.apply(select(Concept))