feat: defer description template resolution

[nieomylnieja]

Motivation

Built-in rules rendered description templates during construction, even when no validation error or validation plan needed the description. This caused avoidable work during rule construction.

Summary

• Added lazy, cached description-template rendering for failed validations and validation plans.
• Migrated all template-backed built-in rules and removed the eager rendering helper.
• Kept static and custom rule descriptions unchanged.

Testing

• Added unit coverage for deferred and single execution, validation and plan consumers, template failures, setter precedence, and concurrent rule copies.

Release Notes

Added Rule.WithDescriptionTemplate for lazy, cached rule descriptions. Updated built-in template-backed rules to avoid rendering descriptions during construction.

[github-actions]

Test coverage changes:

Package	Before	After	Diff
github.com/nobl9/govy/cmd/govy	0%	0%	✔️
github.com/nobl9/govy/internal	73%	73%	✔️
github.com/nobl9/govy/internal/collections	100%	100%	✔️
github.com/nobl9/govy/internal/inferpath	76%	76%	✔️
github.com/nobl9/govy/internal/messagetemplates	89%	89%	✔️
github.com/nobl9/govy/internal/stringconvert	86%	86%	✔️
github.com/nobl9/govy/internal/typeinfo	94%	94%	✔️
github.com/nobl9/govy/pkg/govy	94%	94%	✔️
github.com/nobl9/govy/pkg/govytest	100%	100%	✔️
github.com/nobl9/govy/pkg/jsonpath	85%	85%	✔️
github.com/nobl9/govy/pkg/rules	99%	99%	✔️