Builder: rehome builder_util

[anshumanmohan]

In #1637, we proposed finding a new home for many of the utilities that currently live in builder_util.py.

In this PR have done that, experimentally, for one such helper: insert_eq. It now lives under ComponentBuilder and is called eq_use. I have piped the changes through to all the Python files, though you may want to look specifically at fifo.py since it benefits from the cleanup of #1664.

Note that I'm calling this utility eq_use to differentiate it from the existing method eq that is also declared on ComponentBuilder. The helper eq just returns a StdEq cell, while this new eq_use variant creates a cell, wires up its ports, and then returns the group and the cell that do all this.

Say we have:

prog = cb.Builder()
fifo: cb.ComponentBuilder = prog.component("fifo")

we used to use the utility via:

util.insert_eq(fifo, cmd, 0, 2) 
# `cmd == 0`, where `cmd` is 2 bits wide.

and now we can do it more directly via:

fifo.eq_use(cmd, 0, 2)

Please let me know what you think, and I'll propagate these changes all over, for all the other utilities.

[rachitnigam]

Looks good! I'm really missing Rust-style traits here which can just add methods on structs without having to define them in the same file. I wonder if there is some sort of idiomatic way to do this in Python but if not, keeping these methods in the ComponentBuilder makes sense to me.

[anshumanmohan]

Thanks for taking a look. I've gone ahead and made this change all over, and as a result, the entire builder_util.py file has gone under the ComponentBuilder class. All the changes have been piped everywhere and the eDSL code is lighter as a result. Ready for another review and then a merge!

[rachitnigam]

Looks like we have some failing tests!

[sampsyo]

Awesome. I definitely think this is headed in the right direction, i.e., adding higher- and higher-level stuff to the builder to make it easier to express the common case.

On @rachitnigam's question:

I'm really missing Rust-style traits here which can just add methods on structs without having to define them in the same file. I wonder if there is some sort of idiomatic way to do this in Python but if not, keeping these methods in the ComponentBuilder makes sense to me.

The way to do this in Python is with mixins. It would look like:

class ComponentBuilderBase:
    # all the basic stuff

class ComponentExtra:
    # high-level fancy stuff like `mem_write_seq_d1_to_reg`

class ComponentBuilder(ComponentBuilderBase, ComponentExtra):
    pass

Multiple inheritance combines the two sets of members together in one exported class. Not sure it's worth it in this case, but we could consider it.

[anshumanmohan]

I'll keep this in mind and return to it in a separate PR! I just don't want to gunk up the works and create more merge conflicts than I can handle