Fix rdconsole Protolathe menu null.mat_efficiency (#22555)

* Please describe the intent of your changes in a clear fashion.
This PR fixes a runtime error (`Cannot read null.mat_efficiency`)
occurring in the R&D console's Protolathe menu
(`/obj/structure/machinery/computer/rdconsole/attack_hand`).

The root cause was a copy-paste error in
`code/modules/research/rdconsole.dm`. Specifically, lines 719 and 721
within the `if(3.1)` block (Protolathe menu rendering) were incorrectly
referencing `linked_imprinter.mat_efficiency` instead of
`linked_lathe.mat_efficiency`.

When a robotics R&D console was linked to a protolathe but not a circuit
imprinter, `linked_imprinter` would be null, causing the error when
attempting to display material costs for designs.

The fix replaces `linked_imprinter.mat_efficiency` with
`linked_lathe.mat_efficiency` at these two lines, ensuring the
Protolathe menu correctly uses the linked protolathe's material
efficiency.
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images of these changes in the PR's description.
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comment with !wip or !review required
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yourself specify the license and original author below.
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changelog as specified in the contributor guidelines

### Asset Licenses
The following assets that **have not** been created by myself are
included in this PR:

| Path | Original Author | License |
| --- | --- | --- |
| icons/example.dmi | ExamplePerson (Example Station) | CC0 |


Fixes SERVER-PROD-39

---------

Co-authored-by: sentry[bot] <39604003+sentry[bot]@users.noreply.github.com>
Co-authored-by: VMSolidus <evilexecutive@gmail.com>

code/modules/research/rdconsole.dm

@@ -716,9 +716,9 @@ won't update every console in existence) but it's more of a hassle to do. Also,
 					dat += "<li><h3>[last_category]</h3>"
 				var/temp_dat
 				for(var/M in D.materials)
-					temp_dat += ", [D.materials[M]*linked_imprinter.mat_efficiency] [CallMaterialName(M)]"
+					temp_dat += ", [D.materials[M]*linked_lathe.mat_efficiency] [CallMaterialName(M)]"
 				for(var/T in D.chemicals)
-					temp_dat += ", [D.chemicals[T]*linked_imprinter.mat_efficiency] [CallReagentName(T)]"
+					temp_dat += ", [D.chemicals[T]*linked_lathe.mat_efficiency] [CallReagentName(T)]"
 				if(temp_dat)
 					temp_dat = " \[[copytext(temp_dat, 3)]\]"
 				if(linked_lathe.canBuild(D))