feat(analysis): support unit-dependent loop starts

[zhen8838]

Why

• Persistent kernels need loop starts and stops derived from mesh coordinates so each unit can own a distinct tile range without losing analysis precision.
• Review found analysis, isl interop, and visitor responsibilities co-located behind misleading names, making these contracts harder to maintain.

What

• Carry bounded mesh coordinates through dimension ranges, loop domains, trip counts, access relations, allocation proofs, and three-argument tile(start, stop, step) round trips.
• Split iteration scopes, access resolution, loop domains, loop terms, isl interop, and type inference into modules matching their responsibilities.
• Add realistic tiled and grid-stride persistent GEMM fixtures; the placed-program inventory covers all analysis families, per-unit trips, access precision, unit partitioning, and memory peaks.

Contract

• tile() accepts two arguments or (start, stop, step). Loop start and extent may depend on bounded unit values; step must be literal because Presburger arithmetic cannot represent a parametric stride.
• Type-inference rules may return TypeInferResults with a value range; bare Type remains valid. RangeMetadata follows the expr.type lifecycle. Inference that does not write type also does not write range.
• TypeInferVisitor and inference_type live in visitor_registry/typeinfer.py; verify, codegen, and cost visitors remain in visitors.py.
• IterationScope, construction, and traversal live in analysis/iteration_scope.py; access resolution lives in analysis/access.py; loop domains live in analysis/loop_domain.py.
• Access and AccessPrecision belong to analysis/access.py; bounded parameters may remain EXACT.
• cardinality is the sole public point-counting entry. An empty parameter context counts as 0; bounded boxes up to PARAM_POINT_LIMIT are enumerated; oversized or nonempty unbounded boxes return None.
• ir/isl_interop.py owns dim/shape-to-isl interop, including index_set; ir/types/dim.py contains only definitions and constructors, ir/types/dim_isl.py is removed, and utils/isl_utils.py remains IR-independent.
• Interop directions are named dim_to_isl_expr, shape_to_isl_domain, and isl_to_dim; normalize_dim and dim_range retain their names. dim_range returns None when no bound is available; unsupported symbolic divisors still raise.
• analysis/loop_terms.py (formerly affine.py) performs HIR-to-LoopTerm conversion without isl. LoopAffineTerm is renamed LoopTerm.
• widest_allowed is public in analysis/access.py; analysis/footprint.py is retained as an empty placeholder for future footprint work.
• resolve_program_geometry and local_duration_ns are public analysis helpers.
• The analysis preflight does not write Expr.type; the previous specification wording claiming it did was corrected.

Risk

• The flat fixture remains WIDENED: loop-term binding does not support floor-div/mod.
• LoopTerm remains a custom tuple-like representation rather than an isl object; this review intentionally only renamed it.
• Analysis still imports three IR internals: ir.hir.specialize._record_complete_bindings, function-local ir.hir.verify._verify_isolated, and ir.types.shard.mesh._positions_layout. Proper fixes require public IR-side APIs, not merely removing underscores.
• Mesh axis naming and x/y/z fallback remain duplicated between parser and printer; they should converge on a shared mesh helper.
• Persistent programs still lack a numerical evaluator reference because per-device MeshCoord evaluation is deferred to issue feat(evaluator): model the mesh so check can reference a coordinate-reading program #138.
• Loop bounds still lack ShapeDim validation, so normalize_dim may retain an invalid static object.
• Parameter boxes above 4096 points make peaks/trips unknown.
• Converters remain outside whole-function range reinference, matching prior behavior; no range consumer reads them.