deltalite: add build-deltalite.yml for riscv64 wheels

[luhenry]

• Package: deltalite
• Version: 0.1.7
• Source: https://github.com/PostHog/posthog (monorepo, rust/deltalite)
• Docs: https://github.com/PostHog/posthog

Compiles deltalite, a pyo3/maturin streaming partition-upsert engine for Delta Lake tables built on the deltalake (delta-rs) crate, into an abi3 wheel. Upstream publishes no riscv64 wheel.

Mirrors upstream's build-deltalite.yml.

Differs from upstream

• Sparse-checks-out rust/ + LICENSE instead of the full posthog monorepo - the Cargo workspace only needs that slice.
• Copies LICENSE into rust/deltalite/python/ - maturin globs licence files next to pyproject.toml, which sits below the repo root.
• Builds via PyO3/maturin-action targeting riscv64gc-unknown-linux-gnu - upstream's matrix has no riscv64 entry.
• Does not run upstream's own differential parity suite: ci-deltalite-python.yml pins deltalake/pyarrow/duckdb and runs it against them, but uv (0.12.13, riscv64) rejects deltalake==1.6.3's only wheel (cp310-abi3-manylinux_2_39_riscv64, correctly served with data-requires-python: >=3.10) as having "no usable wheels" whenever it's resolved by name from an index - reproduced with our registry as both the extra index and, separately, the default index, ruling out an index-priority cause. duckdb/pyarrow (exact cp312-cp312 tags, no abi3) and deltalite's own local-file wheel install both succeed under the same job, isolating the break to uv's abi3-forward-compatibility tag check specifically for a registry-resolved wheel. Of the 8 files under rust/deltalite/python/tests, 7 import deltalake/pyarrow/duckdb (directly or via harness/common.py) and can't run without them; only test_planner.py is self-contained, so it's the one upstream test kept.

Matrix: cp312-abi3 (built once) - pyo3's abi3-py312 feature is unconditional in Cargo.toml.

Testing

• test_planner.py (the one upstream test file with no external deltalake/pyarrow/duckdb dependency).
• Wheel-level: licence-file check.

License: OK

Built on cp312-abi3-manylinux_riscv64; results pending CI.