perf(runtime-tags): stop materializing branch boundary nodes

[DylanPiercey]

Control flow boundaries no longer leave permanent nodes behind, and countable ones stop shipping start comments entirely.

Commit 1: Client rendered templates stop padding the ends of a template or branch body whose edge is if/for/dynamic tag content, and resuming a server rendered branch adopts its real edge nodes rather than retaining the start comment and inserting a text node. A new fixBranchEdges keeps owner ranges valid by repairing their endpoints as nested content moves; debug builds assert range validity at every range read. <show>, <await> and <try> keep their own anchors — a <show> body is inlined into the enclosing scope and the others move their anchors themselves — so they repair their owner's edges rather than being repaired. Costs ~69B brotli of runtime; halves the marker nodes in a resumed page.

Commit 2: Building on that, server rendered if/for branches whose top-level content is statically countable no longer write a start comment per branch — the end marker's new BranchEndCounted symbol carries the per-branch node count and resume walks the range back from the end, generalizing the single-node encoding. An N item loop drops N start comments (~7% of a compressed list page); ~2B brotli of runtime.

[changeset-bot]

🦋 Changeset detected

Latest commit: 3778f47

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 90.35%. Comparing base (302606e) to head (3778f47).
⚠️ Report is 160 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3712      +/-   ##
==========================================
+ Coverage   90.34%   90.35%   +0.01%     
==========================================
  Files         414      414              
  Lines       19746    19833      +87     
  Branches     3615     3652      +37     
==========================================
+ Hits        17840    17921      +81     
- Misses       1367     1370       +3     
- Partials      539      542       +3     

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