tools: auto-attach crowtty when running x86 kernel

[hawkw]

This commit adds code in the x86 bootimage runner to automatically
attach crowtty to the QEMU virtual serial port when running in QEMU
(unless asked politely not to). Doing this required turning crowtty
into a library, so it could be used as a dependency of
x86_64-bootimager.

Since we don't have a working UART driver in the x86 kernel yet (see
#222), the serial port currently only gets us output from the
bootloader, and we can't currently speak SerMux with the running mnemOS
VM. But, I'm gonna go add a serial driver next hopefully.

eliza@theseus ~/Code/mnemos $ just run-x86 --crowtty-verbose
cargo run --package mnemos-x86_64 --target=x86_64-unknown-none --features=bootloader_api -- run --crowtty-verbose
   Compiling regex-automata v0.4.7
   Compiling regex v1.10.6
   Compiling vergen v8.3.2
   Compiling mnemos v0.1.0 (/home/eliza/Code/mnemos/source/kernel)
   Compiling mnemos-x86_64 v0.1.0 (/home/eliza/Code/mnemos/platforms/x86_64/core)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 2.75s
     Running `cargo run --package mnemos-x86_64-bootimager -- --kernel-bin target/x86_64-unknown-none/debug/bootloader run --crowtty-verbose`
   Compiling cfg-if v1.0.0
   Compiling memchr v2.7.4
   Compiling itoa v1.0.11
   Compiling ryu v1.0.18
   Compiling polling v3.7.3
   Compiling polling v2.8.0
   Compiling getrandom v0.2.15
   Compiling nix v0.23.2
   Compiling nix v0.26.4
   Compiling thread_local v1.1.8
   Compiling tempfile v3.12.0
   Compiling uuid v1.10.0
   Compiling tracing-subscriber v0.3.18
   Compiling async-io v1.13.0
   Compiling async-io v2.3.3
   Compiling gpt v3.1.0
   Compiling object v0.32.2
   Compiling serde_json v1.0.122
   Compiling async-signal v0.2.9
   Compiling async-process v1.8.1
   Compiling serialport v4.5.0
   Compiling bootloader v0.11.7
   Compiling serialport v4.0.1 (https://github.com/metta-systems/serialport-rs?rev=7fec572529ec35b82bd4e3636d897fe2f1c2233f#7fec5725)
   Compiling backtrace v0.3.71
   Compiling backtrace-ext v0.2.1
   Compiling miette v7.2.0
   Compiling crowtty v0.1.0 (/home/eliza/Code/mnemos/tools/crowtty)
   Compiling mnemos-x86_64-bootimager v0.1.0 (/home/eliza/Code/mnemos/tools/x86_64-bootimager)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 11.18s
     Running `target/debug/mnemos-x86_64-bootimager --kernel-bin target/x86_64-unknown-none/debug/bootloader run --crowtty-verbose`
    Assuming direct control over the build!
    Building boot image, boot_mode: UEFI, kernel: target/x86_64-unknown-none/debug/bootloader
    Finished bootable disk image [UEFI] in 118.28ms (/home/eliza/Code/mnemos/target/x86_64-unknown-none/debug/mnemos-x86_64-uefi.img)
     Booting mnemOS VM, qemu: qemu-system-x86_64, args: []
  Connecting crowtty...
[  +0004.098695519s] UART BOOT BdsDxe: failed to load Boot0001 "UEFI QEMU DVD-ROM QM00003 " from PciRoot(0x0)/Pci(0x1,0x1)/Ata(Secondary,Master,0x0): Not Found
[  +0004.205543166s] UART BOOT BdsDxe: loading Boot0002 "UEFI QEMU HARDDISK QM00001 " from PciRoot(0x0)/Pci(0x1,0x1)/Ata(Primary,Master,0x0
[  +0004.209001023s] UART BOOT BdsDxe: starting Boot0002 "UEFI QEMU HARDDISK QM00001 " from PciRoot(0x0)/Pci(0x1,0x1)/Ata(Primary,Master,0x0
[  +0005.841023599s] UART BOOT INFO : Framebuffer info: FrameBufferInfo { byte_len: 4096000, width: 1280, height: 800, pixel_format: Bgr, bytes_per_pixel: 4, stride: 1280
[  +0005.841309139s] UART BOOT INFO : UEFI bootloader started
[  +0005.841663228s] UART BOOT INFO : Using framebuffer at 0x80000000
[  +0005.842068224s] UART BOOT INFO : Reading configuration from disk was successful
[  +0005.842356148s] UART BOOT INFO : Trying to load ramdisk via Disk
[  +0005.842728632s] UART BOOT INFO : Ramdisk not found
[  +0005.958230026s] UART BOOT INFO : New page table at: PhysFrame[4KiB](0x2000
[  +0005.959142731s] UART BOOT INFO : Elf file loaded at 0x0000000004f98000
[  +0005.960043464s] UART BOOT INFO : virtual_address_offset: 0xffff800000000000
[  +0005.961674828s] UART BOOT INFO : Handling Segment: Ph64(ProgramHeader64 { type_: Ok(Load), flags: Flags(4), offset: 0, virtual_addr: 0, physical_addr: 0, file_size: 3f524, mem_size: 3f524, align: 1000
[  +0005.963159093s] UART BOOT INFO : Handling Segment: Ph64(ProgramHeader64 { type_: Ok(Load), flags: Flags(5), offset: 3f530, virtual_addr: 40530, physical_addr: 40530, file_size: bbab7, mem_size: bbab7, align: 1000
[  +0005.966445476s] UART BOOT INFO : Handling Segment: Ph64(ProgramHeader64 { type_: Ok(Load), flags: Flags(6), offset: fafe8, virtual_addr: fcfe8, physical_addr: fcfe8, file_size: 179d8, mem_size: 18018, align: 1000
[  +0005.966656455s] UART BOOT INFO : Mapping bss section
[  +0005.968165568s] UART BOOT INFO : Handling Segment: Ph64(ProgramHeader64 { type_: Ok(Load), flags: Flags(6), offset: 1129c0, virtual_addr: 1159c0, physical_addr: 1159c0, file_size: 2b40, mem_size: be70, align: 1000
[  +0005.968348984s] UART BOOT INFO : Mapping bss section
[  +0005.976238970s] UART BOOT INFO : Entry point at: 0xffff800000041740
[  +0005.976821020s] UART BOOT INFO : Creating GDT at PhysAddr(0x45000
[  +0005.977080721s] UART BOOT INFO : Map framebuffer
[  +0005.977782628s] UART BOOT INFO : Map physical memory
[  +0005.978220726s] UART BOOT INFO : Map page table recursively
[  +0005.978546963s] UART BOOT INFO : Allocate bootinfo
[  +0005.978853522s] UART BOOT INFO : Create Memory Map
[  +0005.979163138s] UART BOOT INFO : Create bootinfo
[  +0005.979764544s] UART BOOT INFO : Jumping to kernel entry point at VirtAddr(0xffff800000041740
[2 +0005.979812395s] UART KEYB pseudo-keyboard (SerMux port :2) reading from STDIN
asdf
[2 +0011.139810921s] UART KEYB 5B <- "asdf\n"