How to wire a system for Nios 2 in Qsys?
I've fixed up the design to be work in QSYS. Your error messages:

Error: System.nios2: Reset slave sram_0.avalon_slave_0 not connected to instruction_master.
Error: System.nios2: Exception slave sram_0.avalon_slave_0 not connected to instruction_master.


...were caused by the Properties tab of the nios2 processor - you've evidently selected the SRAM to be the source of the reset/exception vectors, then later renamed the component from sram_0 to sram. I re-selected the sram with the new name and they cleared. The remaining warnings were trivial wiring issues, and forgot to export the SRAM external side connection.

You also had the SRAM source code both with and without the clock/reset fix we spoke about, I dropped the bad one and renamed the QSYS component + tcl to have matching filenames.

Finally set the name of the top level to match Qsys generated output and replaced the source files in Quartus to be the generated .qip file. Analysis and fitter both completed. You don't have any pin mapping in your .qsf file, so the bitstream won't work on any real hardware yet.

You can see the working as I pushed commits along the way.

There's an asynchronous read from memory in the leds module that's preventing a block ram from being inferred, but the device is big enough you can get away without fixing that immediately (would lower resource usage, likely decrease fitter effort if it can be inferred).