applet: add support for applets that have additional requirements. As a concrete example, this (abridged) `pyproject.toml` with a mandatory dependency on `aiohttp`: dependencies = ["aiohttp~=3.8"] [project.entry-points."glasgow.applet"] audio-yamaha-opx = "glasgow.applet.audio.yamaha_opx:AudioYamahaOPxApplet" can now be transformed into the following one with an optional dependency on `aiohttp`: [project.optional-dependencies] http = ["aiohttp~=3.8"] [project.entry-points."glasgow.applet"] audio-yamaha-opx = "glasgow.applet.audio.yamaha_opx:AudioYamahaOPxApplet [http]" If `aiohttp` is not installed or its version is unsatisfying, the CLI shows a placeholder instead of the applet whose `--help` text explains how to install the missing packages. See #234.

applet: kill `all`, use Python entry points to declare applets. `glasgow.applet.all` was an abomination. Now that it is gone, we have several new possibilities: * Out-of-tree applets is the major one. (This commit explicitly prohibits them because the API is not stable or ready for public consumption.) * Applets can now have package dependencies of their own, through their list of optional dependency groups that must be installed. This prevents any further dependency bloat of the software stack. * Applet metadata can at some point be cached to reduce load times. Loading every applet (which we still do, just in a less directly intentional way) is costly, especially on low-power systems or systems with slow disk, and the cost only grows as more applets are developed. Unfortunately, this will continue to be the case so long as `argparse` continues to be used. It might seem odd to move applet's "name" from its source code to `pyproject.toml`. This actually makes sense because it is less its name and more a handle by which it is invoked. It is likely that the handles of out-of-tree applets will collide reasonably often and in that case they will be automatically disambiguated.

applet.audio.yamaha_opx: fix off-by-one.

revC2: Corrected the CAT24M01 part number.

software: use proper `amaranth[builtin-yosys]` dependency. PDM 2.8.1 has fixed the bug that prevented its use before.

cli: in `glasgow voltage`, replace `Monitor` with `Vsense(range)`. This makes it clearer exactly what is monitored.

device.hardware: print causes of `set_voltage()` failure. For example: $ glasgow voltage Port Vio Vlimit Vsense Monitor A 0.0 5.5 0.0 0.0-5.5 B 0.0 3.3 0.0 0.0-5.5 $ glasgow voltage AB 5 E: g.cli: cannot set I/O port(s) AB voltage to 5.0 V (port B voltage limit is set to 3.3 V) It is easy to miss the value in the Vlimit column. The display of causes of the error avoids a source of frustration, and ensures that voltage limit caused errors do not mislead the operator into thinking that their device is faulty.

Replace dependency `crc` with `amaranth.lib.crc` Fixes GlasgowEmbedded/glasgow#371

CI: group all required workflows into one status check. This allows more flexibility in running workflows conditionally.

applet.internal.selftest: ensure CLI exits with code 1 on failure.