perf: improve large-sequence rendering

[AssociatedPrimeIdeal]

Summary

Improves large .seq file opening and waveform interaction.

Issues Fixed

1. Large files no longer open through a TextDocument (seqEditorProvider.ts)

   • Replaced CustomTextEditorProvider with CustomReadonlyEditorProvider.
   • Removed the redundant initial read and parse.
   • Avoids copying the complete file buffer before parsing.

2. Large [SHAPES] sections used excessive temporary memory (reader.ts)

   • Replaced whole-file line splitting with incremental line scanning.
   • Parses shapes directly into growable typed buffers and skips the unused
     section filtering pass.

3. M1 and PNS repeatedly sorted and searched ordered gradient data (m1.ts, pns.ts)

   • Collects gradient points in sequence order and uses forward-only sampling
     cursors, reducing the main paths to linear scans.
   • Fuses PNS padding, differentiation, and low-pass filtering into one pass.

4. Large waveform views performed work proportional to sequence size (drawing.js, interaction.js, state.js)

   • Uses binary/visible-range lookup for tooltips and block boundaries.
   • Limits minimap TR rendering to the available pixel width.

5. Zoomed-out waveform rendering processed sub-pixel raw events (derived-series.js, drawing.js)

   • Adds block-indexed multiresolution min/max summaries for RF and Gx/Gy/Gz.
   • Adds multiresolution ADC occupancy and uniformly sampled RF/ADC phase rendering.
   • Selects detailed or summarized rendering per channel, switching only when
     visible points exceed the available screen-pixel width.

6. Open command supports custom editor tabs (extension.ts)

   • Resolves the active .seq URI from text or custom editor tabs.

Files Changed

• src/editor/seqEditorProvider.ts
• src/extension.ts
• src/pulseq/reader.ts
• src/pulseq/m1.ts
• src/pulseq/pns.ts
• src/editor/webview/assets/state.js
• src/editor/webview/assets/derived-series.js
• src/editor/webview/assets/drawing.js
• src/editor/webview/assets/interaction.js

[Copilot]

Pull request overview

This PR targets performance and memory usage when opening and interacting with large Pulseq .seq files by reducing up-front allocations (notably [SHAPES]), removing repeated sorting/searching work in PNS/M1 calculations, and switching the webview waveform rendering to use block-indexed multiresolution summaries when zoomed out.

Changes:

• Streamline .seq parsing by incrementally scanning lines and parsing [SHAPES] with a dedicated typed-buffer parser (avoids whole-file split + redundant passes).
• Reduce PNS and M1 computation overhead by collecting gradient points in order and using forward-only sampling/cursors, plus a fused PNS model pass.
• Speed up webview interactions/rendering for large sequences via visible-range lookup, minimap TR decimation, and multiresolution waveform overview rendering when point density exceeds pixel budget.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/pulseq/reader.ts	Incremental line scanning and a dedicated [SHAPES] parser using growable typed buffers to reduce temporary memory.
src/pulseq/pns.ts	Refactors PNS to avoid repeated sorts/searches and fuses padding/differentiation/filtering into a forward-only pass.
src/pulseq/m1.ts	Refactors M1 gradient sampling to use a forward cursor and removes per-sample binary searches.
src/editor/seqEditorProvider.ts	Migrates to a readonly custom editor provider and removes redundant initial read/parse; avoids extra buffer copying on read.
src/extension.ts	Improves “open viewer” command by resolving active .seq URIs from both text and custom editor tabs.
src/editor/webview/assets/state.js	Adds waveform overview state creation and reduces minimap TR line work by stepping based on pixel width.
src/editor/webview/assets/derived-series.js	Introduces block-indexed multiresolution min/max summaries and point-prefix indexing for overview rendering decisions.
src/editor/webview/assets/drawing.js	Uses visible-range block bounds and switches channels to overview rendering when visible points exceed pixel budget.
src/editor/webview/assets/interaction.js	Replaces linear block search for tooltips with a binary search helper and includes minimap drag handling state.

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