feat: v2 rewrite, new iterator pattern (take 3) (#251)

* feat: add decoupled v2 multi-axis sequence module

This adds the v2 module with self-contained implementations of:
- AxisIterable: Generic base for axis iteration
- MultiAxisSequence: Generic multi-axis iteration
- TimePlan, ZPlan, GridPlan: Axis-specific implementations
- MDASequence: V1-compatible wrapper with v2 architecture

Key design decisions:
- V2 plan classes are independent (no inheritance from v1)
- Shared types (MDAEvent, Channel, Axis) imported from v1
- Clean separation enables independent evolution

Test status:
- All v1 tests pass (171)
- Core v2 tests pass (129)
- Position sub-sequence tests need additional work

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: add filterwarnings for v2 position sequence deprecation

The test was failing because pytest is configured with filterwarnings=["error"],
which converts the DeprecationWarning from Position.__new__ (when handling
legacy Position.sequence attribute) into an error.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* migration guide

* move enums

* reuse test cases

* moving some v1 stuff

* fix: skip tests on Windows due to tcl issues

* bump min pydantic

* bump again

* skip windows plot

* undo v1 folder

* remove __eq__

* remove doc

* refactor: update MDAEvent contribution structure to include is_relative flag

* fix pydantic issue

* fix docs

* fix tcl

* ignore

* ignore again

* fix duration

* remove dupe

* add grid from poly

* switch runner

* add classmethods

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: tlambert03

.github/workflows/ci.yml

@@ -70,7 +70,7 @@ jobs:
 
   test-dependents:
     name: ${{ matrix.repo }}
-    runs-on: macos-13
+    runs-on: macos-latest
     env:
       UV_MANAGED_PYTHON: "1"
       UV_NO_SYNC: "1"

.pre-commit-config.yaml

@@ -27,6 +27,7 @@ repos:
           - types-PyYAML
           - pydantic >=2
           - numpy >=2
+          - shapely
 
   - repo: local
     hooks: