[Refactor] Rename data structures and functions to be clearer

[milindsrivastava1997]

What to build

Rename overloaded planner abstractions so each name identifies the concept it represents, rather than reusing terms such as "bind," "implementation," and "boundary" across unrelated stages.

Current	Proposed	Reason
Implementation	Realization	A candidate physical form, not source-code implementation.
implementations_for_with	realizations_for_intent	Enumerates ranked physical alternatives for an AggIntent.
Binder / bind	SchemaResolver / resolve_schema	This pass derives schema and resolves column names.
PanePhaseBinding	PaneLayout	Records pane width and origin; does not bind a plan.
BoundaryCoverage	WindowEdgeCoverage	Describes coverage of partial panes at query-window edges.
ExactBoundaryResidual	ExactWindowEdgeResidual	States which boundary the residual covers.
BoundaryKind	PhysicalHandoffKind	Covers network transfer and materialization handoffs.
BoundaryResources	PhysicalHandoffBytes	Byte counters associated with physical handoffs.
boundary_cost	physical_handoff_cost	Costs those physical handoffs.
"comparison boundary"	"comparison scope"	Align documentation with the existing ComparisonScope type.
downstream "boundary"	"planner-runtime contract"	The document defines ownership and exchanged contracts.
internal Models	CandidatePlanningInputs	Holds cost, accuracy, allocation, and evidence inputs.
with_models	new_with_planning_inputs	Makes the injected dependencies explicit.
with_models_and_evidence	new_with_planning_inputs_and_evidence	Same, while distinguishing evidence-bearing construction.

Keep with_* where it is an ordinary fluent builder (with_table, with_update_rate, etc.), and retain IN, WITH, and without where they directly represent SQL or PromQL syntax.

Acceptance criteria

• The logical-to-summary candidate vocabulary uses Realization consistently.
• Schema/name resolution has a single distinct naming family.
• Physical transfers/materialization and query-window edges no longer share the generic boundary name.
• Documentation uses comparison scope and planner-runtime contract for their respective concepts.
• Public renames include migration notes or compatibility aliases where needed.
• Focused tests and documentation links are updated.

Blocked by

None - can start immediately.

[milindsrivastava1997]

@zzylol pls check this.