regalloc_fpr_evict_test.nx

regalloc_fpr_evict_test.nx -- proves linear_scan_fpr's eviction policy fires. Companion smoke to regalloc_evict_test.nx. No public ir_const_f64 / ir_emit_fcast builders exist yet, so we construct Interval entries directly (linear_scan_fpr is leaf- callable: it takes intv + sorted_ids + n + mask + spill_start without touching the Function pointer). The 22-interval workload matches the FPR pool size of 21 (9 caller-clobbered ft-regs after the 3 scratch exclusions + 12 callee-saved fs-regs). Construction: intv[i].end is monotonically decreasing in i, so intv[0] has the LATEST end and intv[21] has the EARLIEST. All crosses_call=0 so the want_cs=0 path is exercised. When intv[21] arrives and the pool is empty, the eviction policy walks active[] backward and finds intv[0] (latest end, in an ft-reg). Since intv[0].end > intv[21].end, evict intv[0]; intv[21] gets that register. Assertion: intv[0].reg == -1 (spilled by eviction) intv[0].slot >= 0 (spill slot assigned) intv[21].reg >= FREG_BASE_T (got a float register)