Refactor TipableVMobject tip placement to avoid curve deformation and transform coupling

[behackl]

Overview

TipableVMobject tip handling currently conflates tip placement with geometry reshaping of the parent curve.

While working on #4503, two code TODOs highlighted behavior that should be tracked explicitly in an issue instead of comments in source.

Current behavior

1. position_tip() directly shifts/rotates the tip mobject to place it at the anchor point.
   • This tightly couples the tip's local transform to parent-side placement logic.
   • It is awkward for custom tip implementations that expect stable local coordinates.
2. reset_endpoints_based_on_tip() calls put_start_and_end_on(...) with tip base points.
   • For non-linear tipable mobjects (e.g. arcs), this can redefine/deform the underlying curve instead of only accounting for the tip attachment.

Desired direction

• Tip placement should be representable as attachment/anchoring logic without mutating the conceptual shape of the underlying curve.
• Endpoint adjustment should trim/extend along the curve direction (or equivalent local rule), not reparameterize the whole curve via put_start_and_end_on.
• Keep tip local transforms as independent as possible from parent placement mechanics.

Related

• PR: Cleanup TipableVMobject: avoid mutable default and fix assign_tip_attr typo #4503
• Existing reports likely touching the same root cause:
  • add_tip() changes shape of ArcBetweenPoints #1801
  • TipableVMobject tips when adding a tip in Manim 0.17.2 #3099