feat: Add wildcard slice expression support

[NatElkins]

Summary

This PR adds support for wildcard slice expressions ([*]) in F# arrays and lists, improving AST clarity for this common slicing pattern.

Problem

The grammar already parsed arr.[*] syntax but didn't create a proper AST node for the wildcard, making it difficult for tools to recognize this as a distinct operation from other slice patterns.

Solution

Added an alias for "*" as wildcard_slice in the slice_range rule:

// Before
slice_range: ($) => choice($._slice_range_special, $._expression, "*"),

// After
slice_range: ($) => choice($._slice_range_special, $._expression, alias("*", $.wildcard_slice)),

Examples

The following F# code now produces clear AST nodes:

let all = arr.[*]           // Select all elements
let row = matrix.[0.., *]    // Select entire row
let col = matrix.[*, 0..]    // Select entire column  

Tests

Added 3 tests to test/corpus/expr.txt:

• Simple wildcard slice
• 2D array row slice with wildcard
• 2D array column slice with wildcard

All existing tests continue to pass.

Related

This addresses one of the gaps identified in #150 (Implementation Status tracking).