Removing a redundant check per the comment in #224.

Introduce the chisel debug check-release-archives command
that verifies that Chisel assumptions avoid the archives hold. For
example, Chisel assumes that parent directories bundled in several
packages in the archive are consistent with one another (i.e. have the
same mode). If the is not the case, we need to flag the issue and
possibly handle it in the slice definitions files.

If an implicit conflict is found in the release but it is handled in the
slice definition then we do not consider it an error and the command
does not fail.

Fixes #158

Use modern Go constructs:

- Replace `interface{}` with `any` (available since Go 1.18)
- Replace 3-clause loop with `range` loop (available since Go 1.22)
- Use `slices` package (available since Go 1.21)

This commits adds maintenance status to a release as the top-level field maintenance in chisel.yaml. The dates there specify the lifecycle of the release in regards to its support status, with and without Ubuntu Pro subscriptions. This enables Chisel to fail if the release and its combination of archives is no longer supported officially and it may lead to security problems. For example, interim releases like mantic and no longer officially supported, and LTSs like focal are only maintained when using ESM which needs an Ubuntu Pro subscription. If no maintained archive is available Chisel will fail, but the user can continue execution by passing --ignore=unmaintained as a CLI flag.

When the dates are into the future it indicates instead that the release is unstable. The user can choose to continue the execution by passing --ignore=unstable as a CLI flag.

Lastly, this commits also allows Chisel to work with interim releases by using the dates described above to change the archive's URL from archive.ubuntu.com to old-releases.ubuntu.com when needed.

Compatibility-wise, Chisel has a list of releases with their default dates so it continues to work with existing chisel.yaml. There will be a window when maintenance is optional for these releases and chisel-releases will be updated. Then, the field will be mandatory.

IMPORTANT: This new version of Chisel will fail to cut Ubuntu 20.04 when Ubuntu Pro is not enabled because the standard archive is unmaintained. Users need to add --ignore=unmaintained or move to a more recent release or use the Ubuntu Pro archives.

The minimal required Go version is bumped to 1.24.6 to fix GO-2025-3956/CVE-2025-47906.
The Go version 1.23.12 cannot be used due to the unavailability in the snapstore.

The version of package github.com/ulikunitz/xz is bumped to v0.5.15 to fix GO-2025-3922/CVE-2025-58058.

This PR introduces scheduled CI runs for the Tiobe TiCS static code analysis.

v3-essential is a new field present for Chisel formats "v2" and "v1".
Note that this does not affect how Chisel does conflict resolution across
dependencies, i.e. Chisel will not take into account architecture specifics
to be smarter about conflicts.

BREAKING CHANGE: This commit changes how yaml is marshalled for tools
such as chisel info. The values of essential and v3-essential are both
marshaled into v3-essential.

This commit reverts the change in aca3b32 that changed the for loop to
use the new range semantics which was not equivalent because we were
mutating the contents of the array in the loop itself.

A test has been added to detect it.