fuzz: fix timeout in `crypto_fschacha20poly1305` #30725

Fixes #30505

This PR fixes a timeout in crypto_fschacha20poly1305 by reducing the number of iterations. I left it running for a while and noticed it speeds up the target and do not impact coverage.

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I think it can be tested by replacing the ConsumeBool() to true which causes a timeout quickly.

--- a/src/test/fuzz/crypto_chacha20poly1305.cpp
+++ b/src/test/fuzz/crypto_chacha20poly1305.cpp
@@ -130,7 +130,7 @@ FUZZ_TARGET(crypto_fschacha20poly1305)
     // data).
     InsecureRandomContext rng(provider.ConsumeIntegral<uint64_t>());
 
-    LIMITED_WHILE(provider.ConsumeBool(), 10000)
+    LIMITED_WHILE(true, 10000)
     {
         // Mode:

Maybe this is a way to know whether a harness can have a possible timeout issue? cc: @maflcko

Please cross-link to the issue (https://github.com/bitcoin/bitcoin/issues/30505)

lgtm ACK 8dec4e1294a6c6895b4fe23f38cd067dc8f2352f

https://cirrus-ci.com/task/6004238088667136?logs=ci#L5367

crypto_fschacha20poly1305                [#83](/bitcoin-bitcoin/83/)	DONE   cov: 3202 ft: 21189 corp: 80/12762b lim: 1368 exec/s: 2 rss: 119Mb

https://cirrus-ci.com/task/6249653828583424?logs=ci#L5217

crypto_fschacha20poly1305                [#83](/bitcoin-bitcoin/83/)	DONE   cov: 3202 ft: 21417 corp: 80/12762b lim: 1368 exec/s: 1 rss: 121Mb

cc: @stratospher

Concept ACK. (running it locally, will ACK after that!) did you check if the timeout happens in crypto_aeadchacha20poly1305 too?

did you check if the timeout happens in crypto_aeadchacha20poly1305 too?

I think we did not have an issue with that yet, but anyway, I'll investigate it and follow-up.

ACK 8dec4e1. saw similar coverage stats (these are from different machines, saw more similar from same machine).

1. on branch #3974498 REDUCE cov: 544 ft: 3788 corp: 250/22Kb lim: 4096 exec/s: 124 rss: 538Mb L: 95/573 MS: 5 ChangeByte-ChangeByte-EraseBytes-ChangeBinInt-InsertByte-
2. on master #3975366 REDUCE cov: 571 ft: 3993 corp: 279/51Kb lim: 4096 exec/s: 148 rss: 829Mb L: 3009/3818 MS: 1 EraseBytes-