Eagerly serialized, partially updatable 2D & 3D line strips (#8650)

This PR makes `LineStrips2D` and `LineStrips3D` eagerly serialized and
partially update-able.

This demonstrates how to migrate an archetype in the simple case.

* DNM: requires #8649  
* Part of #8581

crates/store/re_types/definitions/rerun/archetypes/line_strips2d.fbs

@@ -9,6 +9,7 @@ namespace rerun.archetypes;
 /// \example archetypes/line_strips2d_batch image="https://static.rerun.io/line_strip2d_batch/c6f4062bcf510462d298a5dfe9fdbe87c754acee/1200w.png"
 /// \example archetypes/line_strips2d_ui_radius title="Lines with scene & UI radius each" image="https://static.rerun.io/line_strip2d_ui_radius/d3d7d5bd36278564ee37e2ed6932963ec16f5131/1200w.png
 table LineStrips2D (
+  "attr.rust.archetype_eager": "",
   "attr.rust.derive": "PartialEq",
   "attr.docs.category": "Spatial 2D",
   "attr.docs.view_types": "Spatial2DView, Spatial3DView: if logged under a projection"

crates/store/re_types/definitions/rerun/archetypes/line_strips3d.fbs

@@ -9,6 +9,7 @@ namespace rerun.archetypes;
 /// \example archetypes/line_strips3d_batch title="Many strips" image="https://static.rerun.io/line_strip3d_batch/15e8ff18a6c95a3191acb0eae6eb04adea3b4874/1200w.png"
 /// \example archetypes/line_strips3d_ui_radius title="Lines with scene & UI radius each" image="https://static.rerun.io/line_strip3d_ui_radius/36b98f47e45747b5a3601511ff39b8d74c61d120/1200w.png"
 table LineStrips3D (
+  "attr.rust.archetype_eager": "",
   "attr.rust.derive": "PartialEq",
   "attr.docs.category": "Spatial 3D",
   "attr.docs.view_types": "Spatial3DView, Spatial2DView: if logged above active projection"