feat: namespaces

[jcmfernandes]

What does this PR do?

Replaces the prefix/suffix-based option generation with namespace-based generation. Instead of generating top-level functions with prefixes (e.g., WithMyOption()), it generates methods on a namespace struct (e.g., OptionNs.MyOption()).

Key Changes:

• Removed -prefix and -suffix command-line flags
• Added -namespace flag (defaults to ${option}Namespace)
• Changed generated API from top-level functions to namespace methods
• Updated template to generate namespace struct and methods
• Fixed implementation type naming to avoid collisions across different option types in the same package
• Added ARGV to generated files showing the command used for generation

Example:

Before:

//go:generate go-options -prefix=With -option=Option config
cfg := newConfig(WithMyInt(123))

After:

//go:generate go-options -namespace=OptionNs -option=Option config
cfg := newConfig(OptionNs.MyInt(123))

Motivation

The prefix/suffix approach polluted the global namespace with many top-level functions. The namespace approach:

1. Better organization: Groups all related options under a single namespace
2. Cleaner global namespace: Only one namespace variable instead of dozens of functions
3. Modern API design: Similar to how other Go libraries organize their APIs
4. Better discoverability: IDE autocomplete shows all options when typing OptionNs.

Additional notes

Breaking Change

This is a breaking change that removes the -prefix and -suffix flags entirely. Users must:

1. Update their go:generate directives to use -namespace instead of -prefix/-suffix
2. Update their code to use the namespace-based API (OptionNs.MyField() instead of OptionMyField())

Implementation Details

• Template changes (render.gotmpl): Added namespace struct generation and changed functions to methods
• Implementation type naming: Fixed to include option type name prefix to avoid collisions (e.g., optionMyIntImpl vs myOptMyIntImpl)
• Generated file headers: Now include the command-line arguments used for generation

How to test the change?

make test