Expanded demo tests to cover more public methods and functions from go/types and go/token packages, as discovered via `go doc`.
**go/types additions:**
- Type comparison functions: Identical, AssignableTo, Comparable, ConvertibleTo
- Interface checking: Implements, AssertableTo
- String formatting: TypeString, ObjectString with qualifiers
- Lookup utilities: LookupFieldOrMethod, NewMethodSet
- Type utilities: IsInterface, Default, Id
**go/token additions:**
- Utility functions: IsExported, IsIdentifier, IsKeyword, Lookup
These additions provide better coverage of the packages' public APIs and demonstrate proper usage patterns for interface conversions and method calls.
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Co-authored-by: luoliwoshang <51194195+luoliwoshang@users.noreply.github.com>
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