feat: support conditional flags

[thesayyn]

• Plain strings are always included (backward-compatible)
• (flag, constraint) tuples are included only when the running Bazel version satisfies the semver constraint
• Pre-release versions are normalised (8.0.0-rc1 → 8.0.0) so >=8 matches RC builds
• Invalid constraint strings are a hard error at invocation time

---

Changes are visible to end-users: yes

• Searched for relevant documentation and updated as needed: yes
• Breaking change (forces users to change their own code or config): no
• Suggested release notes appear below: yes

ctx.bazel.build() and ctx.bazel.test() now accept (flag, constraint) tuples alongside plain strings in flags and startup_flags.

  ctx.bazel.build(
      "//...",
      flags = [
          "--always_present",
          ("--notmp_sandbox", ">=8"),
          ("--some_legacy_flag", "<7"),
      ],
  )

Test plan

• New test cases added

[thesayyn]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 0904eedbc4

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".