Absurdly long forced mate evaluations in some games

Nobody has claimed this yet.

I've been processing some database dumps (namely to find a forced-mate to win% curve a la lichess-org/lila#11148), but I found some games have evaluations with *absurdly* large forced mate evaluations. Like, into the millions or even *billions* of full-moves. (For comparison, the longest known forced mate is [#549 ignoring the 50-move rule](https://lichess.org/study/bFo2OOVC).)

Here are some games from December 2025 my preprocessing script has found since I added a check for this:
- https://lichess.org/m8ktnmt5#121
- https://lichess.org/8ehpTJZs#100
- https://lichess.org/bz61a9mQ#71
- https://lichess.org/iVUEQC5Z#99
- https://lichess.org/yo5dkSjL#79
- https://lichess.org/5mu39F0E#90
- https://lichess.org/QbzNk4uo#112
- https://lichess.org/51cSsamg#100
- https://lichess.org/myUJjgY6#99
- https://lichess.org/z0sldOqC#108
- https://lichess.org/OLgYrSS0#90
- https://lichess.org/WfheBnwg#100
- https://lichess.org/nTE2OipQ#113
- https://lichess.org/nTE2OipQ#115
- https://lichess.org/johafN5y#120
- https://lichess.org/c50AmF8W#86
- https://lichess.org/JNrWQ3xZ#104

~~It's still processing right now, around half done.~~ (Done now, remaining games added to the above list.) I also use the Gaviota DTM tablebases for <=5 piece endgames without castle rights before checking the `%eval` comment, so there may be more.

Here are also some points in my processed datasets from before I added the check. I don't have the game IDs, and I can't guarantee these are all from separate games.
- November 2025
- #16066, White won, Blitz
- #-1019672388, Black won, Blitz
- October 2025
- #1049214217, White won, Rapid
- #1002858761, White won, Blitz
- #844849361, White won, Blitz
- #1021005695, White won, Blitz
- #-1015295096, Black won, Rapid
- #1020408300, White won, Blitz
- #-1072213380, Black won, Bullet
- #-806759701, Black won, Blitz
- #981038985, White won, Blitz
- #997796652, White won, Bullet
- June 2022
- Clean, as far as I know.

Start by reproducing the reported evaluations from the linked games and compare the `%eval` comments with the Gaviota DTM results described in the issue. Trace where these values are received and represented in fishnet, then confirm the cause and verify the behavior against the listed examples and the earlier clean dataset.

Written by the indexing model from the issue text.