Merge #153437

153437: asimview: add sha comparison functionality r=tbg a=wenyihu6

Rebased on top of #152959. 
Epic: https://cockroachlabs.atlassian.net/browse/CRDB-49117
Release note: none 

----

Added comprehensive SHA comparison capability to the ASIM viewer tool, enabling
side-by-side comparison of test results between different Git commits.

Major additions:
- New `-sha-compare` flag to enable SHA comparison mode
- `sha_compare.go`: Core logic for managing Git operations, test generation, and file comparison
- `sha_compare.html`: Interactive web interface for SHA comparison with Plotly charts
- File-by-file comparison with visual indicators for identical, different, or SHA-specific files

The tool now supports two modes:
1. Regular file viewer (existing functionality)
2. SHA comparison mode (new) - allows users to select two commits, automatically
   generates test data for both, and provides side-by-side chart comparison

Updated BUILD.bazel and .gitignore to support the new comparison workflow and temporary file storage.

🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

Co-authored-by: wenyihu6 <wenyi@cockroachlabs.com>

Author: craig[bot]

pkg/kv/kvserver/asim/tests/cmd/asimview/BUILD.bazel

@@ -2,8 +2,15 @@ load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
 
 go_library(
     name = "asimview_lib",
-    srcs = ["main.go"],
-    embedsrcs = ["viewer.html"],
+    srcs = [
+        "main.go",
+        "sha_compare.go",
+    ],
+    embedsrcs = [
+        "mma.png",
+        "viewer.html",
+        "sha_compare.html",
+    ],
     importpath = "github.com/cockroachdb/cockroach/pkg/kv/kvserver/asim/tests/cmd/asimview",
     visibility = ["//visibility:private"],
     deps = [

pkg/kv/kvserver/asim/tests/cmd/asimview/README.md

@@ -4,6 +4,8 @@ Interactive web viewer for ASIM test JSON output files with fuzzy search and mul
 
 ## Usage
 
+### Regular File Viewer Mode
+
 ```bash
 # Default: serves files from repo's testdata/generated directory
 go run .
@@ -17,6 +19,24 @@ go run . -port 8081
 
 Then open http://localhost:8080 in your browser.
 
+### SHA Comparison Mode
+
+```bash
+# Enable SHA comparison mode
+go run . -sha-compare
+
+# With custom port
+go run . -sha-compare -port 8081
+```
+
+Then open http://localhost:8080 in your browser. This mode allows you to:
+
+1. **Generate test data for different Git SHAs**: Enter two commit SHAs and click "Generate Comparison" to run ASIM tests for both commits
+2. **Compare results side-by-side**: Select test files to see JSON data plotted side-by-side for visual comparison
+3. **Automatic Git workflow**: The tool handles switching between SHAs, running tests, and storing results automatically
+
+**Note**: SHA comparison mode requires a clean Git working directory and will temporarily switch between commits to generate test data.
+
 ## Features
 
 - **Fuzzy Search**: Type any part of test name or file name to filter