Implement Python format string parser for str.format() and str.format_map()

[antonsynd]

Location

• src/Sharpy.Core/Partial.Str/Str.cs:328
• src/Sharpy.Core/Partial.Str/Str.cs:339

Description

The `str.format()` and `str.format_map()` methods are not fully implemented. They require a Python format string parser that handles:

• Positional arguments: `"{0} {1}".format(a, b)`
• Named arguments: `"{name}".format(name="world")`
• Format specs: `"{:.2f}".format(3.14)`
• Nested fields and conversions

Currently these methods throw NotImplementedException. Planned for v0.6.