feat(lib): introduce structured templates

[lalvarezt]

Structured Templates (Advanced)

NEW in v0.13.0: Apply multiple inputs to different template sections with individual separators.
This enables powerful scenarios like batch processing, command construction, and data transformation.

use string_pipeline::Template;

// Multiple inputs per template section with different separators
let template = Template::parse("Users: {upper} | Files: {lower}").unwrap();
let result = template.format_with_inputs(&[
    &["john doe", "jane smith"],  // Multiple users for first section
    &["FILE1.TXT", "FILE2.TXT"]   // Multiple files for second section
], &[" ", ","]).unwrap();         // Space separator for users, comma for files
assert_eq!(result, "Users: JOHN DOE JANE SMITH | Files: file1.txt,file2.txt");

// Template introspection
let sections = template.get_template_sections(); // Get template section info
assert_eq!(sections.len(), 2); // Two template sections: {strip_ansi|lower} and {}

Key Features:

• 🎯 Flexible Input: Each template section can receive multiple input values
• ⚙️ Custom Separators: Individual separator for each template section
• 🔍 Introspection: Examine template structure before processing
• 🏗️ Batch Processing: Perfect for processing multiple items per section

[lalvarezt]

@alexpasmantier care to have a look, this solves some of the issues related to multiple selection in television