Add Node 24 support (minimal)

[dmartin-figma]

Adds Node 24 to the test/release matrix and bumps @figma/nodegit to 0.28.0-figma.10 so subsequent tag pushes produce ABI v137 prebuilts (alongside existing 108/115/127).

Why

figma/figma is moving to Node 24 (see #768808 in the main monorepo). Cursor agents already run on Node 24 (/opt/cursor-agent/node is v24.5.0, ABI v137); the in-monorepo bot-bot CI image also moves to Node 24 with that PR. Both fail today because no v137 prebuilt exists in figma-nodegit.s3.amazonaws.com. This PR unblocks the prebuilt publish.

What

Commit	Change
update test ssh key + use updated key for tests	Cherry-picked from upstream (053e0bff, 35596615). Rotates the GH-quarantined SSH key + decodes from test/id_rsa.enc at runtime so secret scanning doesn't re-flag it. Required for the 3 SSH cred tests to pass.
Add Node 24 to build matrix	One-line addition to the Linux + macOS matrices.
Bump C++ standard to C++20 for Node 24+	utils/defaultCxxStandard.js: select C++20 when process.versions.modules >= 137. V8 13.x's cppgc/macros.h and v8-local-handle.h require C++20 features (P0732, requires-clauses).
Switch from @axosoft/nan to upstream nan@^2.26.2 for Node 24 V8 API support	@axosoft/nan@2.20 predates V8 13.x. Upstream nan@2.26.2 includes the v8::Local::GetIsolate and PropertyCallbackInfo::This() deprecation fixes. Updates binding.gyp include path accordingly.
Use clang-14 on Linux CI for Node 24 V8 C++20 features	clang-10 (default in ubuntu:20.04) lacks P0732 (class template argument deduction in concepts) which V8 13.x's cppgc macros use.
Pin Linux runner to ubuntu-22.04 + Bump Linux container to ubuntu:22.04	ubuntu:20.04 container had DNS resolution issues against the ubuntu-latest host runner. ubuntu:22.04 ships clang-14 natively, eliminating the need for an extra apt repo.
Add explicit constructors to OdbObjectsData inner structs for C++20 aggregate rules	C++20 tightened aggregate-init rules; CommitInfo/BlobInfo/TagInfo need explicit member ctors when paired with user-declared move constructors.
Bump to v0.28.0-figma.10	Version bump for the new tag.

Test Plan

• Linux Tests (18, 20, 22, 24) green — confirmed in Add Node 24 to build matrix #18 with these same commits
• macOS Tests (18, 20, 22, 24) green — confirmed in Add Node 24 to build matrix #18 with these same commits
• After merge: tag v0.28.0-figma.10, verify figma-nodegit.s3.amazonaws.com/nodegit-v0.28.0-figma.10-node-v137-{linux-x64,darwin-arm64}.tar.gz published
• Re-run figma/figma#768808's bot-bot CI to confirm Node 24 install works end-to-end