Remove version-forcing and use 0.cabal whenever it exists

[neilmayhew]

See #118 for the suggestion

[neilmayhew]

cc @andreabedini

[neilmayhew]

This doesn't seem to be working quite right yet

[Copilot]

Pull request overview

This PR removes the metadata-driven “force version” mechanism and instead standardizes on using a stored revisions/0.cabal file whenever it exists, plus adds a CLI command to rewrite a Cabal file’s version.

Changes:

• Remove force-version from meta.toml schema and downstream data flow/metadata output.
• In source preparation, copy revisions/0.cabal into the extracted source tree when present.
• Add foliage rewrite-version VERSION FILE command and remove the old UpdateCabalFile module.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
foliage.cabal	Wire in new CmdRewriteVersion module; drop removed UpdateCabalFile.
app/Main.hs	Route new RewriteVersion command to its handler.
app/Foliage/UpdateCabalFile.hs	Delete old Cabal rewriting helper module.
app/Foliage/PrepareSource.hs	Copy revisions/0.cabal into the source tree when available; remove force-version gating.
app/Foliage/PreparePackageVersion.hs	Remove pkgVersionForce from prepared package representation.
app/Foliage/Options.hs	Add rewrite-version subcommand and Command constructor.
app/Foliage/Meta.hs	Remove force-version field from PackageVersionSpec and TOML codec.
app/Foliage/CmdRewriteVersion.hs	New implementation for rewriting a Cabal file’s version from CLI input.
app/Foliage/CmdImportIndex.hs	Stop emitting packageVersionForce in imported metadata.
app/Foliage/CmdBuild.hs	Stop emitting forced-version metadata field.

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[neilmayhew]

I didn't deprecate use of the force-revision field. If present, it will simply be ignored. However, we can remove all uses of it from cardano-haskell-packages and update the add-revision script not to insert it, so it's very unlikely that it will ever be present in future.

[neilmayhew]

I took out the forced-version field from foliage/packages.json in the built repo. As far as I can see, it wasn't being used for anything. We could have inferred it by comparing the upstream cabal file and the revision-0 one, but that seems like overkill for something we aren't using anyway.