JOSS 2.0 in-review

A round of fixes and improvements prompted by JOSS review

• Methods no longer lose relative accuracy when data is rescaled; a test now enforces f(a*x) == a*f(x)
• lineardiff now supports axis, defaults to CLARABEL, and is fast enough to join suggest_method and the optimization demo notebook
• robustdiff's search space is leaner and faster, now that log_r has a natural set point at 0
• optimize no longer swallows warnings, which surfaced a batch of numerical bugs since fixed, including in splinediff, estimate_integration_constant, and robust_rme
• Windows are constrained to odd sizes, because evenness silently degraded results; windows also now forced to touch or overlap so samples cannot be left uncovered between windows nor at the array tail
• Missing values and variable timesteps now raise explanatory errors instead of often silently returning NaNs
• Dependency list corrected, with a few min versions added
• General hardening and bugfixes: spectraldiff wavenumber indexing was off-by-one, rtsdiff no longer aliasies on circular domains; savgoldiff now measures length along correct axis; butterdiff now uses second-order sections; polydiff bounds window size against degree; and waveletdiff no longer NaNs out at threshold 0