Use const for hand-written iterator objects in 00generator.ts

[ASDAlexander77]

Summary

• The // DO NOT PUT CONST, otherwise you can't edit comments in 00generator.ts (main1/main2/main3) dated back to the bug fixed in Give const bindings with bound-method fields (generators) real identity storage #244: a const binding with no backing storage couldn't correctly mutate an object's state through a bound method (like .next() mutating this.nextIndex/this.iterationCount).
• That's fixed. Verified const bindings to these hand-written iterator objects now advance state correctly across manual .next() calls. Switched let it → const it in all three main* functions and removed the stale comments — it is never reassigned in any of them anyway.
• Scanned the rest of the test suite for similar stale "don't use const" style comments; this was the only file with this pattern.

Test plan

• 00generator.ts (compile + JIT) passes with const iterator bindings
• Full suite: 351/351 JIT + 355/355 compile, 0 failures

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