Introduce EditContext to simplify parameter editing code paths

[sastraxi]

Summary

Fixes #253.

A MIDI-CC advanced mapping has a physical-control range. It does not change the plugin parameter range.

Before this PR, a mapping could narrow the parameter grid and could clamp the local value when MOD changed the mapping. This could make the LCD show a value different from MOD.

Changes

• Add EditContext for the parameter, commit function, and editor range.
• Use the declared plugin range for UI and NAV edits.
• Use the physical mapping range for encoder and MIDI edits.
• Keep UI edits on the WebSocket path.
• Keep physical edits on the MIDI CC path.
• Change binding ranges without changing the parameter value or confirmed value.
• Use the instance ID and symbol as the parameter dialog cache key.
• Rename common.parameter_steps to common.parameter_editing.
• Update tests and input documentation.

User result

• A plugin dialog can reach the full plugin range.
• A physical control uses the range selected in MOD-UI.
• Changing a MIDI mapping does not change the current plugin value.
• A failed send can still roll back to the last MOD-owned value.
• Two plugins can open dialogs for parameters with the same name.
• UI and physical edits use the correct transport.

Out-of-scope

Integer value coercion for logarithmic parameters is separate from this PR. It is tracked in #254.

[rreichenbach]

This seems to work with everything I tried.