Link <for> branch owners from the serialized branch list instead of per-branch _ props

[DylanPiercey]

Description

A marker-free <for> serializes its branch scopes as a list on the parent, yet each branch also serializes an identical _: _(parent) owner prop — O(n) redundancy for the common "loop body reads ancestor state" shape.

• The branch list now serializes through an owner-assigning wrapper (_.o(ownerId, scopes)); the resume runtime links each branch's owner from it (a serialized owner still wins, matching marker behavior).
• When markers are statically off, the per-branch _ prop is elided outright; when the marker reason is runtime-dependent (e.g. of=input.items), _ serializes behind that same guard, so marker-off renders drop it and marker-on renders keep today's behavior.
• With the owner gone, branches with nothing else to say are elided from the fill entirely.

Example (for-tag-static-value-with-closure): Aa:[_(2),…,_(5)] plus four {_:_(1)} fills becomes just Aa:_.o(1,[_(2),…,_(5)]).

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: 7e7299f

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 94.30%. Comparing base (9849a13) to head (7e7299f).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3353   +/-   ##
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  Coverage   94.29%   94.30%           
=======================================
  Files         388      388           
  Lines       53085    53153   +68     
  Branches     4237     4240    +3     
=======================================
+ Hits        50058    50125   +67     
- Misses       2998     3000    +2     
+ Partials       29       28    -1     

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