fix: prevent tilemap coordinate overflow

[joeykchen]

Tile placement multiplied int32 coordinates before widening: 67108864 * 64 became zero instead of 4294967296. Bounds also overflowed at MaxInt32+1 and MinInt32-1.

Perform coordinate and bounds arithmetic in int64, then check that returned dimensions and runtime-consumed edges fit int before narrowing. Unrepresentable bounds return the existing false result. A second cleanup replaces four repeated min/max branches with built-ins. Compact records, sorting, callback order, and negative tile-size conventions remain unchanged.

Validation: new placement and extreme-boundary regressions fail on the old implementation and pass after the fix. Native tilemap/root tests, pure tilemap tests/root compilation, wasm root compilation, and Linux 386 pure tilemap compilation pass with Go 1.26.5. A native-only overlay additionally exercises simulated 32-bit range rejection; no execution of a 386 binary is claimed.

Runtime metadata was regenerated twice. Source patches combine cleanly with #2003; regenerate export.types with make generate-runtime when combining pending runtime PRs.

Combined validation of all five fixes passed with Go 1.26.5: 79 host packages, codegen and interpreter submodules, pure/wasm root compilation, and actual Web binding wasm tests. Two full generation runs produced identical diffs; all six external Godot outputs were unchanged.

[fennoai]

Reviewed the complete fixed range 03576e6c0bbead9e73736482539dd321f5521206...21e96c06419853a66ce74ac93566582bf1a0e3fb, including the generated runtime metadata. Focused validation passes with go test ./internal/tilemap and go test .; the attempted 386 test build is blocked by pre-existing missing native binding symbols outside this diff.

No concrete, actionable correctness or regression issues were found in the changed tilemap arithmetic, bounds handling, generated metadata, or call-site integration. The patch is correct based on the fixed diff and the passing focused host tests.