feat: add no_upgrade config option for environment installation

[Maxusmusti]

Add a no_upgrade field to EnvConfig that controls whether the --no-upgrade flag is passed to prime env install. This prevents the install command from upgrading existing packages, preserving locked dependencies (e.g., from uv.lock). A useful option to have for when orchestrator auto-installs the specified environments in config (currently just uses the default behavior of prime env install).

Follow-up PR to PrimeIntellect-ai/prime#295 (CC @JannikSt)

Changes:

• Add no_upgrade: bool = False to EnvConfig
• Update install_env() to accept and pass --no-upgrade flag
• Update get_env_ids_to_install() to return dict with no_upgrade settings
• Update all callers (eval, orchestrator, synthesize) to use new API

Usage

In your rl.toml config, add no_upgrade = true to any environment that should preserve locked dependencies:

[[env]]
id = "will/wordle"
no_upgrade = true

  [[env]]
  id = "other/env"
  # no_upgrade defaults to false, so this env will use normal upgrade behavior

This is useful when:

• You have a uv.lock file and want to preserve exact dependency versions
• An environment's dependencies conflict with your project's pinned versions
• You need reproducible builds with consistent package versions

---

Note

Introduces a configuration to preserve locked dependencies during environment installation.

• Adds env.no_upgrade: bool to EnvConfig and documents it in CHANGELOG.md
• Updates install_env(env_id, no_upgrade=False) to pass --no-upgrade to prime env install when set
• Changes get_env_ids_to_install to return a {env_id: no_upgrade} map and merge duplicates preferring True
• Updates callers in eval, orchestrator, and synthesize to use the new API; orchestrator merges train/eval envs with no_upgrade=True precedence

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[Maxusmusti]

Hi @JannikSt, lmk if there's anything you'd like me to add or change here when you get a chance, thanks!