chore: v0.1.12.dev3 dev release

[mikasenghaas]

Summary

• Bump version from 0.1.12.dev2 to 0.1.12.dev3
• Add release notes covering 17 commits since v0.1.12.dev2

Key changes in this release

• max_total_tokens parameter for MultiTurnEnv
• max_turns_in_context and summarize_turns standard tool for smarter RLM context management
• Hardened RLM root-tool transport (removed unsafe pickle deserialization)
• headers/extra_headers support in endpoints.toml
• Several bug fixes (opencode config, composable mkdir quoting, tool args, math rubric timeout)

🤖 Generated with Claude Code

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Note

Low Risk
Low risk: this PR only bumps the package version and adds release notes; no runtime logic changes are included.

Overview
Bumps verifiers.__version__ from 0.1.12.dev2 to 0.1.12.dev3.

Adds RELEASE_v0.1.12.dev3.md documenting highlights and the changelog for the v0.1.12.dev3 dev release (features, fixes, and RLM security hardening included in prior commits).

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