feat: add Windows ARM64 (win32-arm64) platform support

[npiesco]

Add prebuilt native binary support for win32-arm64, enabling @duckdb/node-api to run on Windows ARM64 devices (e.g. Snapdragon X).

Build system:

• Add fetch_libduckdb_windows_arm64.py to download the ARM64 DuckDB prebuilt library (duckdb.h, duckdb.lib, duckdb.dll)
• Add OS==win and target_arch==arm64 conditions to all three binding.gyp targets (fetch_libduckdb, duckdb, copy_duckdb_node)

Platform package:

• Add @duckdb/node-bindings-win32-arm64 package (os: win32, cpu: arm64)
• Register it as an optionalDependency in @duckdb/node-bindings
• Add explicit case in the runtime platform loader (duckdb.js)

CI pipeline:

• Add windows_arm64 workflow dispatch input
• Add windows_arm64 job targeting the windows-arm64 GitHub Actions runner, with ARM64-specific Node.js headers and node.lib

Documentation:

• Update README.md with the new package in all relevant sections (docs, npm links, version update checklist, DuckDB upgrade checklist)

Tested locally on Windows ARM64 hardware:

• Bindings: 19 test files, 261 tests passed
• API: 1 test file, 92 tests passed
• End-to-end smoke test: instance creation, queries, prepared statements, structs, lists, dates, Parquet/CSV roundtrips all pass

[jraymakers]

Thanks for this PR! It mostly looks good, but there's a problem with the image tag that prevents it from running in GitHub Actions.

[npiesco]

@jraymakers feedback noted and incorporated

[npiesco]

@jraymakers taken care of