fix: preserve TCO through error values

[He-Pin]

Rebased onto current master at b4c667d5 (Add lazy array views for large stdlib arrays (#814)).

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 directly on TailCall as primitive/ref fields: optional &&/|| validation plus optional error value throw.
• Avoid linked continuation nodes, wrapper values, and per-wrapper check objects on deep recursive paths.
• Keep the trampoline hot path simple: TailCall.resolve carries pending checks in local parameters and returns immediately when no final check is pending.
• 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.

Performance notes

• No allocation is introduced for delayed boolean/error continuations; the only state is stored on the existing TailCall.
• The resolve loop is tail-recursive, monomorphic in the common path, and uses null/reference checks rather than allocating small continuation objects.
• Final result validation is skipped entirely for tail calls without delayed checks.

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[2.13.18].compile'
• ./mill --no-server 'sjsonnet.jvm[2.12.21].compile'
• ./mill --no-server 'sjsonnet.jvm[3.3.7].test.testOnly' sjsonnet.FileTests sjsonnet.TailCallOptimizationTests
• ./mill --no-server 'sjsonnet.js[2.13.18].compile' 'sjsonnet.wasm[2.13.18].compile'
• ./mill --no-server 'sjsonnet.native[2.13.18].compile'
• ./mill --no-server '__.checkFormat'
• ./mill --no-server '_.jvm[_].__.test'
• ./mill --no-server '_.js[_].__.test'
• ./mill --no-server '_.wasm[_].__.test'
• ./mill --no-server '_.native[_].__.test'
• git diff --check

Rebase note

The previous CI failures were caused by the stale base: EncodingModule.scala had an unused UTF_8 import on that revision. Current master uses that import, so rebasing fixes those compile failures.