fix: preserve TCO through error values

[He-Pin]

Rebased onto current master at 7eb796f (chore(deps): bump actions/cache from 4.3.0 to 5.0.5 (#819)).

Motivation

error value evaluates value immediately before throwing. That value is a tail position for auto-TCO and explicit tailstrict, but resolving a TailCall inside the error expression would re-enter the trampoline from the current function body and can bring back recursive stack growth for deep error f(n - 1) chains.

error value also must not be treated as an unconditional non-recursive exit. A function like local f() = error f() has no base case; auto-TCOing it would turn the existing max-stack diagnostic into an infinite trampoline loop.

Implementation

• Evaluate tail-position error value with tail-call support and attach a delayed error-value continuation to the returned TailCall.
• Store delayed result continuations as fixed-slot state: optional &&/|| validation plus optional error value throw.
• Avoid linked continuation nodes and per-wrapper check objects on deep recursive paths; the trampoline combines a small final container in place, which is more JIT- and GC-friendly.
• Preserve continuation order:
  • inner error value preempts any outer boolean check or outer error throw
  • inner boolean validation runs before an outer error throw
  • redundant outer boolean validations collapse after the innermost boolean check
• Update auto-TCO exit analysis so Expr.Error recursively inspects its value expression instead of always counting as a non-recursive exit.

Tests

New golden tests cover:

• auto-TCO and explicit tailstrict through error value
• lazy unused arguments through a 10000-deep recursive error f(n - 1, unused) chain
• boolean-check-before-outer-error ordering
• inner-error-before-outer-bool ordering
• nested boolean continuation ordering
• a non-tail lhs negative case
• an error value expression whose non-recursive exit is inside the error value
• a no-exit error f() case that must keep the max-stack diagnostic

Verification

• ./mill --no-server 'sjsonnet.jvm[3.3.7].compile'
• ./mill --no-server 'sjsonnet.jvm[3.3.7].test.testOnly' sjsonnet.FileTests
• ./mill --no-server 'sjsonnet.jvm[3.3.7].test.testOnly' sjsonnet.TailCallOptimizationTests
• ./mill --no-server __.checkFormat
• git diff --check