Fix duplicate PRIMARY KEY on composite primary keys

[dbczumar]

Problem

A composite (multi-column) primary key compiles to two PRIMARY KEY
clauses, which Cloudflare D1 rejects:

CREATE TABLE labels (
    conv TEXT NOT NULL PRIMARY KEY,   -- inline, from get_column_specification(first_pk=True)
    key  TEXT NOT NULL,
    v    TEXT,
    PRIMARY KEY (conv, key)           -- table-level, from create_table_constraints (len > 1)
)
-- D1: "more than one primary key" (SQLITE_ERROR, code 7500)

get_column_specification inlines PRIMARY KEY for the first PK column whenever
first_pk=True, while create_table_constraints also emits the table-level
constraint for composite keys — so composite PKs get both. Single-column keys
are fine (the table-level one is suppressed), which is why the existing tests
didn't catch it.

Fix

Inline PRIMARY KEY only for a single-column key; composite keys are emitted
solely as the table-level constraint (exactly what create_table_constraints
already intends). One guarded condition in get_column_specification.

After:

CREATE TABLE labels (
    conv TEXT NOT NULL,
    key  TEXT NOT NULL,
    v    TEXT,
    PRIMARY KEY (conv, key)
)

Single-column PKs are unchanged (id TEXT NOT NULL PRIMARY KEY).

Tests

Adds test_create_table_composite_primary_key (the existing PK tests only cover
single-column keys). Full unit suite green (21 passed). Verified end to end
against a live D1 instance: the table now creates successfully.

---

Found while running Alembic migrations for a real app on D1. Two related
reflection gaps I hit in the same effort, in case they're useful as follow-ups
(happy to send PRs): get_foreign_keys omits the referred_schema key that
SQLAlchemy's reflection accesses (raises KeyError when reflecting a table with
an FK), and get_unique_constraints isn't implemented (Alembic's
batch_alter_table calls it). Both are reflection-only and orthogonal to this
DDL fix.

[CollierKing]

Thanks for the PR!

Added a follow-up commit with live integration coverage for this fix on both connection paths:

• REST API integration: creates a composite primary-key table via SQLAlchemy, inserts/selects a row, then drops it.
• Worker integration: adds a matching Worker endpoint and pytest coverage for the same composite primary-key flow.

Validation run locally:

• uv run ruff check tests/integration/test_restapi_integration.py examples/workers/src/entry.py tests/integration/test_worker_integration.py
• uv run ruff format tests/integration/test_restapi_integration.py examples/workers/src/entry.py tests/integration/test_worker_integration.py --diff
• uv run pytest --disable-socket --allow-unix-socket tests/unit/test_dialect.py -q -> 21 passed
• uv run pytest tests/integration/test_restapi_integration.py -q -> 80 passed
• Worker integration full file with Node v22.17.1 on PATH -> 65 passed

[CollierKing]

Thanks again for the PR and the follow-up issues, addressed those in #27.

All changes in v0.3.11

Cheers!