Track drop points by MIR Place

[coord-e]

Motivation

• Replace the previous ad-hoc Local-only drop-point representation with MIR Place so implicit drops are tracked at the correct place granularity.
• This ensures correct restoration of drop obligations for moved closure environments and removes brittle projection-less-local workarounds.

Description

• Change DropPoints to store mir::Place<'tcx> in before_statements, after_statements, after_terminator, and after_terminator_extra, and make DropPoints generic over the MIR lifetime.
• Convert liveness-derived Local sets into mir::Place<'tcx> in DropPointsBuilder::build and adapt APIs to insert/remove/query places.
• Update the basic-block Analyzer to use DropPoints<'tcx>, add drop_place/drop_after_terminator operations, and route all implicit-drop handling to work with mir::Place<'tcx> across statements and terminators.
• Add drop_place to the refinement Env and make drop_local delegate to it, and update local_def and RustCallVisitor to produce/consume places (including restoring closure environment-drop obligations at the precise place).

Testing

• Ran cargo check, which completed successfully.
• Ran cargo fmt and git diff --check, which reported no issues.
• Ran cargo test (UI test suite), which failed due to environment limitations (missing external verifier/solver and docker usage in wrappers), causing many UI tests to fail; failures are due to the test environment, not obviously due to this change.

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Codex Task

[coord-e]

Superseded by #155, which builds on this branch's Place-based DropPoints and adds the actual #121/#122 fix (splitting partially-moved locals into their still-owned sub-places in the drop-point production) plus regression tests. Verified that this branch alone did not reject the false-assertion cases; #155 does, with the full UI suite green. Closing in favor of #155.

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