logs: replace every fmt::print with a lg call instead (#1368)

Favors the `lg` namespace over `fmt` directly, as this will output the
logs to a file / has log levels.

I also made assertion errors go to a file, this unfortunately means
importing `lg` and hence `fmt` which was attempted to be avoided before.
But I'm not sure how else to do this aspect without re-inventing the
file logging.

We have a lot of commented out prints as well that we should probably
cleanup at some point / switch them to trace level and default to `info`
level.

I noticed the pattern of disabling debug logs behind some boolean,
something to consider cleaning up in the future -- if our logs were more
structured (knowing where they are coming from) then a lot this
boilerplate could be eliminated.

Closes #1358

decompiler/analysis/reg_usage.cpp

@@ -212,7 +212,7 @@ RegUsageInfo analyze_ir2_register_usage(const Function& function) {
     // also useful to know, written and unused.
     for (auto reg : op->write_regs()) {
       if (op_info.live.find(reg) == op_info.live.end()) {
-        // fmt::print("op {} wau {}\n", op->to_string(function.ir2.env), reg.to_string());
+        // lg::print("op {} wau {}\n", op->to_string(function.ir2.env), reg.to_string());
         op_info.written_and_unused.insert(reg);
       }
     }
@@ -222,4 +222,4 @@ RegUsageInfo analyze_ir2_register_usage(const Function& function) {
   ASSERT(result.op.size() == ops->ops.size());
   return result;
 }
-}  // namespace decompiler
+}  // namespace decompiler