stack use improvements (towards nanox execution)

[ryankurte]

attempting to fix the app execution on the nanox (no luck so far)

further improvements to stack frame sizes in the hope that the less efficient ISA caused a recurrence of the 8kb of stack issue, blocking inlining of large functions in the same stack frame and swapping to per-field init of large objects. this doesn't appear to have helped.

testing targets for nanosplus/nanox devices to try and isolate the error from the ISA

• build for nanox with thumbv7m-none-eabi target (adds DIV and MOD instructions), this runs correctly in simulator, @yhql tested this still appears to fail on device
• tested compiling for nanosplus with thumbv7m-none-eabi and thumbv6m-none-eabi targets, both run fine on the physical nanosplus and simulator, suggesting the issue is specific to the nanox OS / hardware

---

stack frames before:

 ADDR        SIZE   STACK  NAME                                                          
 0xc0df9a89  132    3488   Function::clear                                               
 0xc0df6559  420    3264   <impl Mul<&RistrettoPoint> for &Scalar>::mul                  
 0xc0de60ad  16436  3192   sample_main                                                   
 0xc0de00d9  4428   3160   Engine<DRV,RNG>::ring_update                                  
 0xc0de14a1  5172   2344   Engine<DRV,RNG>::tx_summary_update                            
 0xc0de3df5  492    2168   Engine<DRV,RNG>::ring_init                                    
 0xc0de2935  5312   1608   Engine<DRV,RNG>::update                                       
 0xc0dfb8f9  904    1176   mc_transaction_types::masked_amount::v2::get_blinding_factors 
 0xc0dfa2a9  768    1176   Hkdf<H,I>::new    

stack frames after:

 0xc0deebe5  348   3264   <impl Mul<&RistrettoPoint> for &Scalar>::mul                  
 0xc0df30a5  1140  1944   RingSigner::ring_update                                       
 0xc0de1c31  2320  1448   Summarizer<_>::add_output_unblinding                          
 0xc0de0419  4120  1416   Engine<DRV,RNG>::update                                       
 0xc0de18c1  612   1328   RingSigner::ring_init                                         
 0xc0df51ed  700   1152   mc_transaction_types::masked_amount::v2::get_blinding_factors 
 0xc0df3c49  588   1152   Hkdf<H,I>::new                                                
 0xc0de2541  712   1152   Summarizer<_>::finalize                                       
 0xc0df17b5  4464  1112   Event::parse                                                  
 0xc0de1431  464   1112   Engine<DRV,RNG>::memo_sign 

[ryankurte]

Current dependencies on/for this PR:

• main
  • PR update vendor/mob to latest #3132 #21
    • PR stack use improvements (towards nanox execution) #23 👈
    • PR WIP: handle unrecognised APDUs / interaction with ledger-live while nanoapp is running #22
    • PR library integration improvements #24

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[ryankurte]

not working on the nanox yet but tested on the nanosplus / may as well land these improvements to stack allocation to avoid slip against main