Revert "bump rust to 1.82.0 (#3308)"

[brooksprumo]

Problem

I'm experiencing SIGILL crashes due to invalid opcodes. Maybe it's related to the recent rust 1.82.0 upgrade? Getting a revert PR going so it'll be ready as needed.

I started up two nodes with master, just after the upgrade of rust to 1.82.0 (f8b33755f6b08d03f020bbeae4fd9724f2a407d3). Both nodes crashed. Upon investigating the syslog, both had:

Oct 25 20:20:00 localhost kernel: [6027386.359788] traps: solRspndrGossip[2670083] trap invalid opcode ip:5560731be7d7 sp:7ec4429bd840 error:0 in agave-validator[55607252e000+246e000]
Oct 25 20:20:24 localhost systemd[1]: sol.service: Main process exited, code=killed, status=4/ILL

I built the binaries locally on each machine. I retried on one of the machines three times, and got the same crash each time. I then kept the same commit checked out and built with rust 1.81.0 and there were no more crashes.

Summary of Changes

This reverts commit ed5e30d.

[steviez]

I'm in favor of this to restore stability to master.

I also think we should cut v2.1 with rust 1.81. As Brooks called out, there is seemingly some change of behavior between rust versions that we need to address before bumping back to rust 1.82 anywhere

[brooksprumo]

Merging. Once the UB fix lands, we can re-upgrade rust to 1.82.0. This unblocks everyone running validators on master.