feat(core): Add Supplier and Consumer function callback support

[tzolov]

Add support for no-argument Supplier and single-argument Consumer function callbacks in the Spring AI core module. This enhancement allows:

• Registration of Supplier callbacks with no input (Void) type
• Registration of Consumer callbacks with no output (Void) type
• Support for Kotlin Function0 (equivalent to Java Supplier)
• Handle empty properties for Void input types in schema generation
• Enhance FunctionCallback builder to support Supplier/Consumer patterns

Additional changes:

• Add test coverage for both Supplier and Consumer callbacks in various scenarios
• Enhance TypeResolverHelper to support Consumer input type resolution
• Support lambda-style function declarations for improved ergonomics
• Add test cases for void input/output handling in OpenAI chat model
• Include examples of function calls without return values
• Add support for parameterless functions through Supplier interface

Resolves #1718 , #1277 , #1118, #860

[markpollack]

Refactored some of the long methods so that it reads more cleanly. Added 'final' to the kotlin delegate classes.

[markpollack]

in the docs, the section "Customization Options" was empty, so I removed it.

[markpollack]

merged in 432954dad7f7c3a33117848a4259bc7076865c5f