Support optional parameters and PostgreSQL defaults in PugSQL

[aemonge]

When a query function accepts arguments with PostgreSQL defaults (e.g.
limit_count INTEGER DEFAULT 5), PugSQL requires all parameters to be passed
explicitly, causing runtime errors when omitted.

Requested Feature:

• Permit missing keyword arguments to resolve as None or be omitted entirely.
• Optionally add syntax such as :param? to clarify optionality in templates.
• Ensure PostgreSQL default values in functions are honored automatically.

Benefit:

Simplifies calling stored procedures and aligns Python usage with Postgres
semantics. Minimizes boilerplate for functions where most arguments already
define sensible defaults.