Skip workspace settings entries whose URI has no filesystem path

[Copilot]

In a mixed multi-root workspace (a local file: folder plus a virtual root such as MicroPico's pico:), uris.to_fs_path("pico:") returns None, which flowed into normalize_path() → pathlib.Path(None) and raised TypeError, blocking initialization of the Pylint, Black, and isort servers.

Changes

• server.py — ToolServer.update_workspace_settings() now resolves the filesystem path into a local variable and skips entries where it is None; file: roots are registered unchanged.

for setting in settings:
    workspace_path = uris.to_fs_path(setting["workspace"])
    # Virtual workspace roots, such as "pico:", have no local
    # filesystem path, so they cannot be registered here.
    if workspace_path is None:
        continue

    key = normalize_path(
        workspace_path,
        resolve_symlinks=self.config.resolve_symlinks,
    )

• tests/test_server.py — regression test in TestUpdateWorkspaceSettings feeding file:///local-workspace (mocked to /local-workspace) alongside pico: (mocked to None), asserting no raise, a single registered workspace, and its workspace / workspaceFS values.

Scope

Deliberately limited to filesystem-based workspace registration. Document synchronization and stdin-based tool execution are untouched, so documents from a virtual root can still be delivered and processed by consuming language servers — they simply fall back to the existing cwd-based settings lookup rather than a workspace-specific entry. Virtual-filesystem mirroring is out of scope here.