BattleSearch: Fix pathological regex

[larry-the-table-guy]

PCRE lookahead was causing the regex to be pathologically slow.

The lookahead was introduced by #7801 , the purpose of which I (eventually) inferred to be to handle out-of-order player IDs.
I.e., you do /battlesearch alice, bob and also want to match battles where p1 was bob and p2 was alice.

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Cases I've tested: files with no matches, and search 1 ID w/ matches in either slot, and search 2 ID w/ matches in either order.

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Measured perf on directory with 500K files, 8GB, all non-matches.
Low-end cacheless NVMe SSD.

File cache was cleared each run with echo 3 | sudo tee /proc/sys/vm/drop_caches.

Before: 100% CPU usage, 1MB/s disk read.
After: 20% CPU usage, 500MB/s disk read.

$ rg --version
ripgrep 14.1.1 (rev 4649aa9700)

features:+pcre2
simd(compile):+SSE2,-SSSE3,-AVX2
simd(runtime):+SSE2,+SSSE3,+AVX2

PCRE2 10.43 is available (JIT is available)

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When testing, I had to disable a couple permission checks, disable ripgrep's gitignore behavior and import Monitor to actually be able to run this. Those changes are visible at larry-the-table-guy@b519ef6 . That is the code I tested and measured with, and then I copied the relevant changes to this PR branch.

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Chatlog was also touched by #7801, but it seems that feature has since been moved to a DB, so IDK if it's worth changing that one as well.