Seed Revise's cache source hash with a UInt, so 32 bit runs can revise

[davidanthoff]

Revise passes the precompile cache header's content hash to hash as a UInt64. The seed hash takes is a UInt, 32 bits wide on a 32 bit platform, so on every x86 leg Revise's package callback dies:

MethodError: no method matching hash(::UInt64, ::UInt64)
  at cache_src_id (packages/Revise/src/pkgs.jl:138)
  at parse_pkg_files → watch_package → …

Every test item that loads a package in that process then reports the failed callback as its own error, which is how this surfaces on JuliaMCP's rc~x86 legs in items that have nothing to do with Revise.

This replaces the first version of this PR, which fixed it by editing packages/Revise/src/pkgs.jl. That was wrong — packages/ holds git subtrees that are never edited by hand. Re-vendoring is no help either: the bug is upstream's, and the vendored copy is already at 3.16.4, the latest tag, whose src/pkgs.jl:138 still reads cache_src_id(inc) = hash(inc.fsize, UInt64(inc.hash)).

So the method is supplied where testprocess/TestItemServer/src/pkg_imports.jl assembles the Revise module, right after the vendored packagedef.jl is included. It is added, not redefined: a definition with the vendored signature is a method overwrite, which Julia rejects outright while a package precompiles, and the second commit here fixes exactly that regression from the first —

WARNING: Method definition cache_src_id(Any) in module Revise at packages/Revise/src/pkgs.jl:138
         overwritten at testprocess/TestItemServer/src/pkg_imports.jl:106.
ERROR: Method overwriting is not permitted during Module precompilation.
  24769.9 ms  ? TestItemServer

Precompilation is warn-only on the path a test process takes, so TestItemServer still loaded — at the cost of reloading the whole vendored stack from source in every test process, and of a precompile banner on its stderr that landed in whatever a test item captured. That is what reddened the 64 bit legs: the assertions that a process's output carries no ANSI escapes, the coverage items whose processes then went unanswered, and the recycling items that timed out on the extra startup.

Both call sites (Revise/src/loading.jl:118, Revise/src/pkgs.jl:192) pass a Base.CacheHeaderIncludes, so a method on that type is strictly more specific and wins dispatch without touching upstream's cache_src_id(::Any). Guarded to 32 bit, where the bug is — on 64 bit the vendored definition already computes the right value, and leaving its dispatch and invalidation exactly as upstream ships them is one less thing to reason about. inc.hash is a UInt32, so UInt(inc.hash) is an exact widening on either word size; isdefined covers the internal Base type, whose shape is unchanged from 1.11 through nightly.

The suite had nothing asserting that TestItemServer's cache is actually built — the breakage only surfaced through unrelated assertions about process output — so test/test_testserver_precompile.jl precompiles the version-matched test process environment and fails on a ?. It uses Base.compilecache rather than Pkg.precompile: that rebuilds unconditionally, so a cache another item already wrote cannot short-circuit it, and it reports failure as a return value instead of exiting 0. Verified to fail on the overwriting form and pass on this one.

Smoke-tested under both 1.12 and 1.12~x86: the environment precompiles ✓ on both, the two methods coexist with the 32 bit one winning dispatch and computing the same value, and the color-output, coverage and worker-recycling items all pass.

Found while auditing the stack for Julia 1.13 readiness; like #79 this is a word-size bug the rc legs merely made visible. An upstream Revise PR follows, so the override can be dropped at the next re-vendor.

Note for the x86 legs: they will keep failing "Coverage without coverage roots" after this merges. That failure's stack trace points into ~/.julia/packages/TestItemControllers/…, i.e. the registered TestItemControllers that juliati runs the suite on, not the checkout — it is present on main today and clears only once a release carrying this fix is registered.

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