Run-length encode scope-ref lists and repeated fills in the resume payload

[DylanPiercey]

Description

Loop-heavy pages serialize O(n) bookkeeping per iteration: branch-scope lists ([_(2),_(3),…,_(201)]), closure subscriber sets, and identical per-branch fills ({_:_(1)} repeated). Branch scope ids allocate contiguously, so these are arithmetic runs:

• Arrays/Sets that are entirely scope references with a constant id step serialize as _.s(from,count[,step]) (≥3 items).
• A scope fill textually identical to the previously emitted one collapses into a negative repeat token in the fill array ({_:_(1)},-199), which the resume runtime expands into per-scope copies. Collapse is purely textual and post-hoc — refs/channel side effects already ran — and is disqualified whenever a fill writes anything identity- or position-sensitive (newly tracked objects, scope-bound registered calls), so distinct-but-equal objects are never aliased.

Measured on a 200-item <for> reading a parent <let>, the resume script drops from ~5.6 KB to roughly constant size for the bookkeeping portion. The decoder additions cost ~150 B min in the shared runtime.

Checklist:

• I have read the CONTRIBUTING document and have signed (or will sign) the CLA.
• I have updated/added documentation affected by my changes.
• I have added tests to cover my changes.

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🦋 Changeset detected

Latest commit: 6fd8bd0

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@marko/runtime-tags	Patch

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.29%. Comparing base (9849a13) to head (6fd8bd0).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3352      +/-   ##
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- Coverage   94.29%   94.29%   -0.01%     
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  Files         388      388              
  Lines       53085    53180      +95     
  Branches     4237     4246       +9     
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+ Hits        50058    50147      +89     
- Misses       2998     3003       +5     
- Partials       29       30       +1     

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