Sled-agent: detect switch backend (tofino, softnpu, et al) at runtime - #11237

control: job assigned to worker 01M1QHHM4DBWVZEMXF6F1A9RWG [factory aws, i-0e92b85267a5928fc] (queued for 42 s)
...
task: starting task 0: "setup"
task: process exited: duration 4128 ms, exit code 0
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task: starting task 1: "rust-toolchain"
task: process exited: duration 15515 ms, exit code 0
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task: starting task 2: "authentication"
task: process exited: duration 16 ms, exit code 0
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task: starting task 3: "clone repository"
task: process exited: duration 14871 ms, exit code 0
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task: starting task 4: "build"
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| info: running `cargo check --bins` on zone-setup (369/369)
| warning: profile package spec `blake2b_simd` in profile `dev` did not match any packages
| warning: profile package spec `rust-argon2` in profile `dev` did not match any packages
|     Checking uzers v0.12.2
|     Checking zone-setup v0.1.0 (/work/oxidecomputer/omicron/zone-setup)
|     Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.73s
| 
| real    13:01.912520316
| user    20:23.199606743
| sys      4:10.231468247
| trap        0.328843809
| tflt        0.548652588
| dflt        0.843047586
| kflt        0.004389218
| lock  1:20:24.305807681
| slp   1:34:39.350460040
| lat        57.227251161
| stop     4:01.292878489
task: process exited: duration 918534 ms, exit code 0
|W| found 0 output files