chore: remove the @cartesi/devnet package

[brunomenezes]

Summary

Removes the @cartesi/devnet package. Nothing uses it anymore: the CLI generates its contracts with @cartesi/wagmi-plugin (caff871), and the SDK fetches the Anvil state from the cartesi/dave release (1fa0162). The local devnet the CLI runs against (Anvil, with fork support) does not change. Only the package goes away.

PS: Once this is merged, the published 2.x prereleases could be deprecated on npm. This needs an owner of @cartesi/devnet. cc: @tuler

Changes

• Deletes packages/devnet/ and the devnet workflow. bun.lock drops the workspace and its nested dependencies.
• Removes the @cartesi/devnet entries from .changeset/pre/: deletes the 29 changesets that bumped only devnet, and removes the devnet line from fluffy-taxis-attend.md, keeping its @cartesi/sdk bump. See Notes.
• Removes the Foundry install from the release workflow. Nothing in bun run build or bun test calls forge, anvil or cast anymore.
• Removes the devnet package from README.md and CLAUDE.md, including the README note that the build needs Anvil.

Notes

• In pre mode, Changesets v3 moves each versioned changeset to .changeset/pre/ instead of deleting it, so it can go into the stable changelog. changeset version still reads these files and checks every package they name against the workspace:

  changeset version → readChangesets (+ .changeset/pre/) → assembleReleasePlan → throws on a missing package
  

  With the package removed and .changeset/pre/ untouched, changeset status fails with:

  Error: Found changeset pre/all-rings-care for package @cartesi/devnet which is not in the workspace
  

  So the Release workflow would fail at its next changeset version. The docs allow updating or deleting these files before pre exit (prereleases, migration). The cleanup is in its own commit, so it can be dropped if needed.

• The cleanup does not affect the devnet versions and tags already published to npm and git. It only removes devnet's entries from the stable changelog generated when pre mode ends, and with the package gone there is no stable devnet release to write them to.

• No changeset is included: a removed package has nothing to version.

• Local checks: biome ci, bun install --frozen-lockfile and bun run build pass. bun run test gives 325 pass / 1 skip / 0 fail, unit and integration. changeset status gives the same output as before the removal.

[changeset-bot]

⚠️ No Changeset found

Latest commit: bf2256b

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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