Legacy version of ugly_hacks_to_avoid_creating_duplicate_modules, pre…

… NIR overhaul of amaranth.

Merge branch 'upstream_follower' into ugly_hacks_to_avoid_creating_du…

…plicate_modules, in the process completely recreating the mechanism for de-duplicating identical modules.

It is still far from cleanly implemented, and it might be slightly less efficient than last version. I should revisit these ideas.

hdl.mem: warn about indexing memories with a `Value`.

CI: automatically publish GitHub releases.

sim.pysim: Only close VCD/GTKW files if we opened them ourselves.

Fixes amaranth-lang#1107.

hdl._dsl: fix using 0-width `Switch` with integer keys.

Fixes amaranth-lang#1133.

Implement RFC 39: Warn on `Case()` and `matches()` with no patterns.

Implement RFC 5: Remove `Const.normalize`.

Closes amaranth-lang#754.

Release version 0.4.

setup: fix documentation URL for releases.