Rank __init__.py results lower in workspace symbol search

[yslim-030622]

Summary

Fixes #2465

When a symbol is re-exported from __init__.py, workspace symbol search currently surfaces both the __init__.py re-export and the original definition at equal priority. This means users often land on the re-export rather than the actual definition.

This PR applies a single stable sort pass at the workspace symbol response site to push __init__.py results after non-__init__.py results, while keeping both visible. The fuzzy relevance ordering within each group is preserved (Rust's sort_by_key is a stable sort).

Scope: workspace symbol response path only (workspace_symbols.rs). No changes to fuzzy matching, go-to-definition, shared export search logic, dedup behavior, or any other LSP feature.

Changes

• pyrefly/lib/lsp/non_wasm/workspace_symbols.rs: add a stable sort by is_init() after assembling the result list, with a single comment explaining the invariant.
• pyrefly/lib/test/lsp/lsp_interaction/workspace_symbol.rs: add regression test test_workspace_symbol_prefers_non_init_result that opens both an implementation module and its package __init__.py, queries for the shared symbol, and asserts the ordering invariant holds.
• pyrefly/lib/test/lsp/lsp_interaction/test_files/tests_requiring_config/workspace_symbol_prefer_non_init/: minimal fixture package with one definition in implementation.py and one re-export in __init__.py.

Test Plan

• New LSP interaction test covers the ordering invariant end-to-end.
• python3 test.py --no-test --no-conformance (fmt + lint) passes with no new errors introduced.
• Targeted test: cargo test workspace_symbol

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