Fix Windows file URI path conversion for drive-letter paths

[Teakowa]

Goal

Correct file_uri_path on Windows so standard file URIs such as file:///D:/path/to/project.opy resolve to the native Windows path D:\path\to\project.opy instead of /D:/path/to/project.opy.

Context

opy-rs v0.1.15 currently decodes a standard Windows file URI with a drive letter into a path that retains the URI-leading slash. This produces /D:/..., which is not a valid native Windows path for the provider workflow.

The defect is observable through Wright's first-party OPY provider integration: Windows installed/native Wright workflows fail once opy-rs resolves the incoming source URI to /D:/.... This is an opy-rs owner defect in file URI/path handling and should not be worked around in Wright.

Related consumer work: wrightkit/wright#245 and wrightkit/wright#252.

Scope

• Fix file_uri_path handling for Windows drive-letter file URIs.
• Preserve correct handling for non-Windows paths and other already-supported file URI forms.
• Add regression coverage for standard Windows drive-letter URIs, including file:///D:/....
• Verify the provider path remains compatible with the LPP file-URI contract used by Wright.

Non-goals

• Adding URI/path normalization workarounds in Wright.
• Changing the LPP wire contract.
• Broad refactoring of provider path handling unrelated to this defect.
• Changing source-language semantics or project-loading ownership.

Acceptance Criteria

• On Windows, file:///D:/path/to/project.opy resolves to the native drive-letter path D:\path\to\project.opy without a leading /.
• Existing Unix-style file URI behavior remains unchanged.
• Regression coverage demonstrates the previous /D:/... result would fail.
• Wright's Windows OPY provider workflow can consume the corrected path without a consumer-side workaround.
• The fix is released in opy-rs so Wright can update to the owner-provided correction.

Dependencies / ownership

• Owning repo: opy-rs.
• Consumer verification: wright after the fixed opy-rs release is available.