ast,checker: add type checking for param of fn passed as generic arg

[dy-tea]

Fixes #26195.

[dy-tea]

Adventofcode has a cgen issue, will look into it.

[spytheman]

This PR managed to find implicit type conversion bugs in stats.v , which is a very good sign.
Thank you @dy-tea .

[spytheman]

the vlib/v/slow_tests/inout/publish_shared_object_method_call.vv failure can be worked around with:

 fn (shared eb EventBus[T]) publish(event_type EventType, data T) {
        lock eb {
                for _, subscriber in eb.subscribers[event_type] {
-                       subscriber(data)
+                       subscriber[T](data)
                }
        }
 }

but imho should not have to, the type should have been inferred

[dy-tea]

Good that it is finding issues. Been kind of going in circles fixing a test and a different one breaks for a while :/

[dy-tea]

Just rebased to master for now.

[dy-tea]

I believe this is also a type promotion bug:

 FAIL  [1096/2677] C:  1448.9 ms, R:     0.000 ms vlib/v/tests/comptime/comptime_infix_assign_test.v
>> compilation failed:
vlib/v/tests/comptime/comptime_infix_assign_test.v:20:21: error: cannot use `int` as `u64` in argument 1 to `u64_to_hex`
   18 |             else { return '' }
   19 |         }
   20 |         return u64_to_hex(item, len)
      |                           ~~~~
   21 |     } $else $if T is $array {
   22 |         mut hex := ''