feat: add schema field type classes for FTS

[jhamon]

Summary

Add user-friendly schema field type classes for defining index schemas with typed fields.

Closes SDK-101

Field Types

Class	API Type	Key Parameters
TextField	string	filterable, full_text_searchable
IntegerField	integer	filterable
FloatField	float	filterable
DenseVectorField	dense_vector	dimension, metric
SparseVectorField	sparse_vector	metric
SemanticTextField	semantic_text	model, field_map

Usage Example

from pinecone import TextField, DenseVectorField, IntegerField

pc.create_index(
    name="my-index",
    schema={
        "title": TextField(full_text_searchable=True),
        "year": IntegerField(filterable=True),
        "embedding": DenseVectorField(dimension=1536, metric="cosine"),
    },
    deployment=ServerlessDeployment(cloud="aws", region="us-east-1"),
)

Test Plan

• Unit tests for each field type serialization (25 tests)
• Tests for default values
• Tests for all configuration options
• mypy type checking passes

Notes

The unit tests use a workaround to load the schema_fields module directly, bypassing the broken import chain in db_control caused by the alpha API changes. This will be fixed in SDK-104/107.

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Note

Low Risk
Low risk: this is additive API surface (new dataclasses + exports) with straightforward serialization logic and unit coverage; minimal chance of impacting existing behavior beyond import/export wiring.

Overview
Adds new schema field type helpers in db_control/models/schema_fields.py (TextField, IntegerField, FloatField, DenseVectorField, SparseVectorField, SemanticTextField, plus SchemaField) that serialize via to_dict() into the API’s expected schema format.

Exports these types through pinecone.db_control.models and top-level pinecone via lazy imports, and adds unit tests validating default values and to_dict() output for each field type (with a temporary direct-module-load workaround in the tests).

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