Per-magazine attachment coordinates + two reload-end glitch fixes - #9

Two small, backward-compatible improvements to scripted_magazines.script, ported onto the current dev (0.2) refactor.

1. Per-magazine attachment coordinates

Right now every mag on a gun shares one offset (s_magazine_positions_<bone>, etc). If two mags for the same gun have different pivots/sizes, one of them sits wrong.

This adds an optional per-mag override: any offset field can be suffixed with the magazine's section —

s_magazine_positions_<bone>_<mag_section> = x,y,z
s_magazine_rotations_<bone>_<mag_section> = x,y,z
s_magazine_scale_<bone>_<mag_section>     = float
s_magazine_parent_bone_<bone>_<mag_section> = <bone>

Resolution per field: if the suffixed key exists it's used, otherwise it falls back to the shared s_magazine_<field>_<bone> key. Guns that only define the shared keys are completely unaffected — same behaviour as before.

The suffixed key is resolved against the loaded mag. During the mid-reload swap the loaded mag is still nil/old, so it falls back to the section the core already captures (incoming_mag_section / pending_swap_mag_section), so the model lands on its final coords immediately instead of jumping when the data commits. The swap path (change_specific_mag_model) applies the per-mag scale for the same reason. Documented with an AK example in 2_guide_on_adding_to_new_anim_sets.ltx.

2. Two reload-end visual glitch fixes

• Skip set_model when the path is unchanged (both update_scripted_magazines and change_specific_mag_model): re-setting a live attachment's model resets its transform until the position/rotation setters re-apply next tick, rendering one frame at the default pose.
• Don't scale the attachment to 0 while a reload is in progress: at reload end the idle anim triggers the no-mag refresh BEFORE the new mag data commits (same frame), which hid the freshly inserted mag until the next animation change (movement). Guarded with magazines.action_in_progress().

Both are guard-only changes; the normal paths are untouched.