Add partial type stubs for dependency-safe modules

[heejaechang]

Summary

• ship an empty py.typed marker and complete sidecar stubs for pgspecial.namedqueries and pgspecial.help.commands
• model named-query configuration structurally so ConfigObj and compatible mutable test configurations retain the required mutation and persistence behavior without Any
• leave the remaining modules unstubbed rather than weaken their contracts: dbcommands and iocommands cross psycopg Query/Params/cursor/adaptation boundaries; main needs exact decorator/handler correlation; root __init__ aggregates that unresolved surface; help.__init__ is empty and adds no useful typing surface

Type completeness

Exact installed-wheel, unfiltered pyright --verifytypes pgspecial --outputjson (no --ignoreexternal):

	Exports	Known	Ambiguous	Unknown	Completeness
main baseline	102	15	10	77	14.7059%
This PR	102	23	9	70	22.5490%

The export-name set is unchanged. helpcommands, NamedQueries, and all seven exported NamedQueries methods move to known types.

Validation

• exact public-name and method surface comparison for both touched modules; focused runtime checks cover factory behavior, mutable named-query state, status strings, and the 166-entry help-table schema
• strict Pyright and mypy positive consumers pass; malformed configurations, singleton assignments, method arguments, and help-table values fail in both checkers
• unflagged mypy.stubtest passes for both touched modules on Python 3.9, 3.12, 3.13, and 3.14; whole-package stubtest remains blocked by the intentionally unstubbed main.py source (default_commands lacks an annotation)
• tox test/coverage environments pass on locally available Python 3.9, 3.12, 3.13, and 3.14
• Python 3.15-dev reproduces clean-main's external libpq failure: no psycopg C/binary wrapper and no system libpq
• Ruff remains exactly at the clean-main 93-error baseline; the new artifacts have no lint or format diagnostics
• wheel built strictly from a fresh sdist; wheel and sdist contain exactly the two .pyi files plus the empty marker, their hashes match the source files, and twine check passes
• policy scan finds no Any, casts, ignores, suppressions, allowlists, checker disables, or runtime .py changes