platform.generic: delegate `GlasgowPlatformPort.direction` to `.io_port`. This doesn't actually change behavior at the moment, but would be the correct implementation if we ever narrow underlying port directions.

applet.interface.spi_controller: modernize API. This commit updates the SPIControllerInterface API to use explicit transaction marking with `async with iface.select():` rather than implicit transaction marking with `iface.xxx(hold_ss=True)`. Also, the implementation of the interface is aligned with that of QSPI applet (work in progress). The gateware is mostly untouched, except for adding the select command, and will be upgraded later. The following applets used implicit transaction marking and had to be upgraded: * memory-25x: tested on hardware * spi-flashrom: tested on hardware * program-ice40: tested on hardware * program-nrf24lx1: tested on hadware * radio-nrf24l01: tested on hardware

applet.program.nrf24lx1: style. NFC

applet: support async context managers in record/replay tests.

applet: support `memoryview` in record/replay tests.

applet.program.ice40_sram: add document reference. NFC

applet.program.ice40_sram: fix typo in `get_done()`.

cli: don't reserve `bitstream` in the arguments namespace. This has caused a conflict with `program-ice40-sram`, and in general is too common of a name to reserve. Of course, we shouldn't be in a situation where these conflicts are possible in first place. Such is life.

cli: speed up startup.

applet.program.avr: improve CLI experience for memory arguments. Before this commit, it was not clear that the filename suffix determines the file format. After this commit this is made clear in the text, and also invalid filenames are rejected at argument parsing stage. Co-authored-by: Collin May