Implement Lua pattern matching for string functions #142

Currently, Lua pattern matching is not implemented in the string library. This limits the functionality of several string functions to plain text operations only.

Missing Pattern Matching Support

The following functions are either missing or have incomplete pattern matching:

• string.find - Only supports plain text search, pattern matching raises TODO implement pattern matching
• string.match - Not implemented (commented out)
• string.gsub - Not implemented (commented out)
• string.gmatch - Not implemented (commented out)

Current Implementation

In findHelper, pattern matching is explicitly unimplemented:

} else {
    l.assert(false) // TODO implement pattern matching
}

Use Cases

Pattern matching is essential for:

• Text processing and validation
• String transformations (gsub)
• Data extraction from structured text
• Cleaning up command output

Example of currently failing code:

-- These would fail with current implementation:
local result = str:gsub("%s+", "")  -- Remove whitespace
local match = str:match("(%d+)")      -- Extract numbers
local iter = str:gmatch("%w+")        -- Word iterator

Impact

This limitation forces users to work around missing functionality with manual string manipulation, reducing the utility of go-lua for text processing applications.

Would it be possible to implement Lua's standard pattern matching engine for these string functions?