Extracting empty log_excerpt

e.g. https://d.kernelci.org/issue/maestro%3A76d4ec715fd28e2b45e3a8ccf6d7a053fbe5821a

```
00:00:15 make --silent --keep-going --jobs=8 O=/tmp/kci/artifacts/build ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- HOSTCC=clang CC=clang
00:00:27 /tmp/kci/linux/arch/arm/boot/dts/arm/integratorap-im-pd1.dts:251.3-14: Warning (dma_ranges_format): /bus@c0000000/bus@c0000000/display@1000000:dma-ranges: empty "dma-ranges" property but its #address-cells (2) differs from /bus@c0000000/bus@c0000000 (1)
00:13:13 make[5]: *** [/tmp/kci/linux/kernel/trace/Makefile:147: kernel/trace/simple_ring_buffer.o.checked] Error 1
00:13:13 make[5]: Target 'kernel/trace/' not remade because of errors.
00:13:13 make[4]: *** [/tmp/kci/linux/scripts/Makefile.build:548: kernel/trace] Error 2
00:17:11 make[4]: Target 'kernel/' not remade because of errors.
00:17:11 make[3]: *** [/tmp/kci/linux/scripts/Makefile.build:548: kernel] Error 2
01:54:32 make[3]: Target './' not remade because of errors.
01:54:32 make[2]: *** [/tmp/kci/linux/Makefile:2139: .] Error 2
01:54:32 make[2]: Target '__all' not remade because of errors.
01:54:32 make[1]: *** [/tmp/kci/linux/Makefile:248: __sub-make] Error 2
01:54:32 make[1]: Target '__all' not remade because of errors.
01:54:32 make: *** [Makefile:248: __sub-make] Error 2
01:54:32 make: Target '__all' not remade because of errors.
```

becomes

```
{
"error": {
"script": "/tmp/kci/linux/kernel/trace/Makefile:147",
"target": "kernel/trace/simple_ring_buffer.o.checked",
"error_type": "kbuild.other",
"log_excerpt": "",
"signature_fields": {
"script": "/tmp/kci/linux/kernel/trace/Makefile:147",
"target": "kernel/trace/simple_ring_buffer.o.checked",
"error_type": "kbuild.other",
"error_summary": ""
}
},
"parser": "kbuild",
"version": "1.0.0"
}
```

Start with the kbuild parser and the sample log linked in the issue, then trace how the failing build line is converted into error.log_excerpt and error_summary. Reproduce the shown input and compare the generated JSON with the expected output, confirming that the extracted excerpt is non-empty and useful.

Written by the indexing model from the issue text.