Preallocate map to save 2 allocations.

```
goos: darwin
goarch: arm64
pkg: github.com/grafana/loki/v3/pkg/logql/log
cpu: Apple M2 Pro
                                       │   old.txt   │              new.txt              │
                                       │   sec/op    │   sec/op     vs base              │
_IPFilter/127.0.0.1-10                   5.048µ ± 0%   4.591µ ± 1%  -9.06% (p=0.002 n=6)
_IPFilter/192.168.0.1-192.189.10.12-10   5.082µ ± 0%   4.634µ ± 0%  -8.83% (p=0.002 n=6)
_IPFilter/192.168.4.5/16-10              4.842µ ± 0%   4.390µ ± 0%  -9.35% (p=0.002 n=6)
geomean                                  4.990µ        4.537µ       -9.08%

                                       │  old.txt   │              new.txt              │
                                       │    B/op    │    B/op     vs base               │
_IPFilter/127.0.0.1-10                   424.0 ± 0%   341.0 ± 0%  -19.58% (p=0.002 n=6)
_IPFilter/192.168.0.1-192.189.10.12-10   424.5 ± 0%   341.0 ± 0%  -19.67% (p=0.002 n=6)
_IPFilter/192.168.4.5/16-10              425.0 ± 0%   341.0 ± 0%  -19.76% (p=0.002 n=6)
geomean                                  424.5        341.0       -19.67%

                                       │   old.txt   │              new.txt              │
                                       │  allocs/op  │ allocs/op   vs base               │
_IPFilter/127.0.0.1-10                   10.000 ± 0%   8.000 ± 0%  -20.00% (p=0.002 n=6)
_IPFilter/192.168.0.1-192.189.10.12-10   10.000 ± 0%   8.000 ± 0%  -20.00% (p=0.002 n=6)
_IPFilter/192.168.4.5/16-10              10.000 ± 0%   8.000 ± 0%  -20.00% (p=0.002 n=6)
geomean                                   10.00        8.000       -20.00%
```

Micro-optimization to use a struct instead of bool to save some bytes.

```
goos: darwin
goarch: arm64
pkg: github.com/grafana/loki/v3/pkg/logql/log
cpu: Apple M2 Pro
                                       │   old.txt   │              new.txt              │
                                       │   sec/op    │   sec/op     vs base              │
_IPFilter/127.0.0.1-10                   4.595µ ± 1%   4.753µ ± 2%  +3.44% (p=0.002 n=6)
_IPFilter/192.168.0.1-192.189.10.12-10   4.611µ ± 1%   4.608µ ± 1%       ~ (p=0.784 n=6)
_IPFilter/192.168.4.5/16-10              4.374µ ± 0%   4.339µ ± 0%  -0.81% (p=0.002 n=6)
geomean                                  4.525µ        4.563µ       +0.84%

                                       │  old.txt   │              new.txt              │
                                       │    B/op    │    B/op     vs base               │
_IPFilter/127.0.0.1-10                   341.0 ± 0%   272.0 ± 0%  -20.23% (p=0.002 n=6)
_IPFilter/192.168.0.1-192.189.10.12-10   341.0 ± 0%   272.0 ± 0%  -20.23% (p=0.002 n=6)
_IPFilter/192.168.4.5/16-10              341.0 ± 0%   272.0 ± 0%  -20.23% (p=0.002 n=6)
geomean                                  341.0        272.0       -20.23%

                                       │  old.txt   │              new.txt               │
                                       │ allocs/op  │ allocs/op   vs base                │
_IPFilter/127.0.0.1-10                   8.000 ± 0%   8.000 ± 0%       ~ (p=1.000 n=6) ¹
_IPFilter/192.168.0.1-192.189.10.12-10   8.000 ± 0%   8.000 ± 0%       ~ (p=1.000 n=6) ¹
_IPFilter/192.168.4.5/16-10              8.000 ± 0%   8.000 ± 0%       ~ (p=1.000 n=6) ¹
geomean                                  8.000        8.000       +0.00%
¹ all samples are equal
```

We can optimize even more here by eliminating the use of the map
and opting to use a 256 len array instead for the lookup.

```
goos: darwin
goarch: arm64
pkg: github.com/grafana/loki/v3/pkg/logql/log
cpu: Apple M2 Pro
                                       │   old.txt   │               new.txt               │
                                       │   sec/op    │    sec/op     vs base               │
_IPFilter/127.0.0.1-10                   4.609µ ± 1%   3.155µ ±  1%  -31.55% (p=0.002 n=6)
_IPFilter/192.168.0.1-192.189.10.12-10   4.621µ ± 2%   3.328µ ± 10%  -27.98% (p=0.002 n=6)
_IPFilter/192.168.4.5/16-10              4.388µ ± 2%   2.947µ ±  1%  -32.84% (p=0.002 n=6)
geomean                                  4.538µ        3.139µ        -30.82%

                                       │   old.txt   │              new.txt              │
                                       │    B/op     │    B/op     vs base               │
_IPFilter/127.0.0.1-10                   272.00 ± 0%   32.00 ± 0%  -88.24% (p=0.002 n=6)
_IPFilter/192.168.0.1-192.189.10.12-10   272.00 ± 0%   32.00 ± 0%  -88.24% (p=0.002 n=6)
_IPFilter/192.168.4.5/16-10              272.00 ± 0%   32.00 ± 0%  -88.24% (p=0.002 n=6)
geomean                                   272.0        32.00       -88.24%

                                       │  old.txt   │              new.txt              │
                                       │ allocs/op  │ allocs/op   vs base               │
_IPFilter/127.0.0.1-10                   8.000 ± 0%   3.000 ± 0%  -62.50% (p=0.002 n=6)
_IPFilter/192.168.0.1-192.189.10.12-10   8.000 ± 0%   3.000 ± 0%  -62.50% (p=0.002 n=6)
_IPFilter/192.168.4.5/16-10              8.000 ± 0%   3.000 ± 0%  -62.50% (p=0.002 n=6)
geomean                                  8.000        3.000       -62.50%
```