hexagon: fix batch buffer bounds and strided copy dispatch

[happyyzy]

Overview

• The batch buffer assertion runs after n_bufs++, so adding the valid 16th buffer aborts. Move the check before the increment, keeping HTP_OP_MAX_BUFS unchanged.
• Equal shapes do not imply contiguous inner elements. The same-shape copy fast paths ignore dimension-0 strides and can copy incorrect values. Require element-size inner strides on both sides; same-type strided copies use the existing HTP strided path.

Requirements

• I have read and agree with the contributing guidelines.
• AI usage disclosure: YES. Codex assisted with the fixes.

[happyyzy]

@lhez @max-krasnyansky, could you take a look at the changes when you have a chance?

[max-krasnyansky]

@happyyzy
I actually ran into those myself while working on #28589
Codex with Terra found a bunch of little things like that :).
So it should be fixed in that big PR and we should be able to merge that soon (going through more reviews and validation).