Copper is riding its longest weekly winning streak since 1994, and the physical market underneath the rally keeps getting thinner. Benchmark prices on the London Metal Exchange notched a 10th straight weekly gain through last Friday, trading near $14,300 a ton and within reach of the record $14,527.50 set in January. On Comex, prices topped $6.70 a pound in August, a fresh all-time high. Behind the run sits inventory that keeps draining: LME warehouse stocks fell for 42 straight days through mid-August, the longest stretch since 2014, and nearly…