[Calyx Emitter] Avoid emitting redundant `write_en = 0` to satisfy `write_together` for reads

Calyx specifies that, for a `seq_memory_d1` if the port `write_en` is driven then `write_data` must also be driven through the `write_together` spec.

However, when the port `content_en` is `1` and port `write_en` is `0`, it implies a read, so `write_data` need not be driven.

Since `write_together` is a safety mechanism can we just tell the emitter to not drive `write_en` when it is `0` and `content_en` is `1`.

For example:

Instead of emitting this (which `papercut` pass complains about):
```futil
group bb0_1 {
std_slice_10.in = for_2_induction_var_reg.out;
arg_mem_0.addr0 = std_slice_10.out;
arg_mem_0.content_en = 1'b1;
arg_mem_0.write_en = 1'd0; <- unnecessary
bb0_1[done] = arg_mem_0.done;
}
```
we emit:
```futil
group bb0_1 {
std_slice_10.in = for_2_induction_var_reg.out;
arg_mem_0.addr0 = std_slice_10.out;
arg_mem_0.content_en = 1'b1;
bb0_1[done] = arg_mem_0.done;
}
```
Since, by default the value will be set to `0`, these two will be equivalent and will satisfy the `write_together` spec as well.

Start at the Calyx Emitter entry point and inspect handling of seq_memory_d1 ports under write_together; reproduce the papercut complaint with the shown read pattern. Confirm completion by emitting the read group without redundant write_en while retaining required write behavior, then run the relevant Calyx emitter and papercut checks.

Written by the indexing model from the issue text.