fix(packaging): ship PEP 561 py.typed marker so downstream type checkers see the annotations

[rohithreddy66666]

Summary

Ships the PEP 561 py.typed marker so downstream mypy / Pyright / VS Code Pylance see the SDK's already-written type annotations. 15-line diff, packaging-only, no .py source touched.

Problem

The SDK is fully type-annotated, but the marker was neither present under src/sochdb/ nor listed in [tool.setuptools.package-data]. Every downstream user's type checker was silently emitting:

error: Skipping analyzing "sochdb": module is installed, but missing library stubs or py.typed marker  [import-untyped]

…and treating the entire sochdb package as untyped Any. Every type hint the SDK ships was invisible to consumers.

Fix

1. Add an empty src/sochdb/py.typed (0 bytes, per PEP 561 §Packaging Type Information — an empty marker is sufficient).
2. Register "py.typed" in the sochdb list under [tool.setuptools.package-data] in pyproject.toml so it lands in the built wheel.
3. Document under a new ## [Unreleased] → ### Fixed in CHANGELOG.md.

No .py source touched. No public API change. No FFI / ABI change. __version__ / __core_version__ unchanged.

Testing — verified locally before pushing

1. Wheel-content check

Confirmed the marker is packaged so downstream pip install receives it:

$ pip wheel . --no-deps -w /tmp/wc
$ python -m zipfile -l /tmp/wc/sochdb-0.8.3-py3-none-any.whl | grep py.typed
sochdb/py.typed                                              0

2. Real mypy before/after

mypy 2.3.0 on Python 3.13, installed into an isolated venv against the built wheel. Same consumer script both times:

# consumer.py
from sochdb import Database
wrong: str = Database("/tmp/db")

BEFORE the fix (marker deleted from the installed sochdb):

consumer.py:1: error: Skipping analyzing "sochdb": module is installed, but
    missing library stubs or py.typed marker  [import-untyped]
Found 1 error in 1 file (checked 1 source file)

→ Database collapses to Any. Two real bugs on line 2 are completely invisible.

AFTER the fix (marker present):

consumer.py:2: error: Missing positional argument "_handle" in call to
    "Database"  [call-arg]
consumer.py:2: error: Incompatible types in assignment (expression has type
    "Database", variable has type "str")  [assignment]
Found 2 errors in 1 file (checked 1 source file)

→ mypy resolves the real Database class from sochdb/database.py, catches the missing _handle argument, and catches the str = Database mismatch. This is the type-safety downstream consumers should have had all along.

3. Standard checks

• python -m compileall -q src/sochdb — clean
• ruff check --select E9,F63,F7 --exclude "src/sochdb/sochdb_pb2*.py" src/ tests/ — All checks passed
• python -c "import tomllib; tomllib.load(open('pyproject.toml','rb'))" — parses; "py.typed" present in [tool.setuptools.package-data].sochdb
• Working-tree diff was byte-verified to have 0 trailing-whitespace lines added or removed (defended against editor format-on-save collateral)

Diff

 CHANGELOG.md   | 13 +++++++++++++
 pyproject.toml |  2 ++
 2 files changed, 15 insertions(+)

Plus a new 0-byte src/sochdb/py.typed.

Rebase note

If a parallel PR also touches ## [Unreleased] in CHANGELOG.md, this one will need a trivial rebase to consolidate under one section — happy to do that on request.