build(devcontainer): pin LLVM tooling to version 23

[plexoos]

Pin the local LLVM devcontainer Feature to version 23 to avoid silent toolchain drift across rebuilds.

Update the installer to prefer a versioned apt.llvm.org suite when it exists, while falling back to the generic suite for current tip versions that do not yet have a dedicated per-version suite.

Fail early when the requested clang-format, clangd, or clang-tidy packages are not available from the selected repository.

[Copilot]

Pull request overview

Pins the devcontainer’s LLVM tooling to a specific major version to prevent silent toolchain changes across rebuilds, and improves the LLVM APT repo selection logic in the feature installer.

Changes:

• Pin the LLVM devcontainer feature to version 23 in .devcontainer/devcontainer.json.
• Update the LLVM feature installer to prefer a per-version apt.llvm.org suite when it exists (with fallback to the generic suite).
• Add an early failure check when requested LLVM packages are not found in the APT cache.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
.devcontainer/features/llvm/install.sh	Adds versioned-suite selection and early package-availability checks for LLVM tooling installs.
.devcontainer/devcontainer.json	Pins the LLVM feature option version to 23 to avoid toolchain drift.

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[plexoos]

@ggalgoczi any comments?