#34759 Remove dead code from bun_router

Dead-code sweep of src/router/lib.rs. Each removed item has zero references across src/, build/debug/codegen/, src/codegen/, src/js/, and packages/ (verified with rg -w). None are #[no_mangle]/extern "C", none appear in any .classes.ts, and none are referenced by string name.

Item	Why it's dead
RouteConfig::from_loaded_routes	Zig fromLoadedRoutes; its only caller was the old dev-server config loader which goes through from_api in Rust
Router::get_public_paths	Zig getPublicPaths; no Rust caller
Router::route_index_by_hash	Zig routeIndexByHash; no Rust caller
TinyPtr::to_string_pointer	Zig toStringPointer; no Rust caller
type RoutePtr = TinyPtr	unused alias (Route.Ptr in Zig, moved to module level for the port, never referenced)
Match::params_iterator	Zig paramsIterator; Rust filesystem_router.rs builds params via PathnameScanner directly
Match::name_with_basename	Zig nameWithBasename; no Rust caller
RouteIndexList::items_public_path	cascade: only caller was get_public_paths
RouteIndexList::items_hash	cascade: only caller was route_index_by_hash (the other items_hash hits in the tree are on the watcher's unrelated SoA types)
RouteIndexList.public_path / .hash columns, RouteIndex.public_path / .hash fields	cascade: write-only once both accessors are gone
Routes.index_id field	cascade: only reader was route_index_by_hash's INDEX_ROUTE_HASH fast path (the load_all local of the same name stays; it feeds dynamic_len)
Route.public_path field	cascade: only reader was the RouteIndex push in load_all; the index-route arm's DirnameStore append existed only to populate it
api::StringPointer re-export, PathnameScanner import	cascade: orphaned by to_string_pointer / params_iterator

Verification

• rg -w <symbol> across the full repo returns only the definition for each primary item
• cargo check -p bun_router and cargo check -p bun_bundler pass, including --target x86_64-pc-windows-msvc (a #[cfg(windows)] debug_assert block was touched)
• bun run rust:check-all: bun_router checks clean on all 10 targets (the bun_jsc build-script failure there is pre-existing on main, unrelated to this change)
• bun bd builds
• bun bd test test/js/bun/util/filesystem_router.test.ts: 29 pass
• bun bd test test/bake/framework-router.test.ts: 35 pass

No test added: this is pure dead-code removal with no observable behavior change, so there is no fail-before case a regression test could cover. The existing router suites above exercise every surviving code path.

Net: -102 lines.