fix(cli): validate transform VRL with --no-environment

[pront]

Summary

This fixes vector validate --no-environment so it still reports transform VRL and condition compilation errors.

The root cause was that --no-environment skipped the normal transform build path where these transform-local checks happen. This PR now validates transforms through their normal build() path during --no-environment, while explicitly skipping aws_ec2_metadata because its build() currently performs environment-dependent work.

Vector configuration

data_dir: "${VECTOR_DATA_DIR}"

sources:
  in:
    type: demo_logs
    format: shuffle
    lines:
      - log

transforms:
  broken:
    inputs:
      - in
    type: remap
    source: |
      .foo = to_int(.bar)

sinks:
  out:
    inputs:
      - broken
    type: blackhole

How did you test this PR?

• Added CLI regression coverage for vector validate --no-environment with an invalid remap program.
• Added CLI coverage showing a condition-based transform is validated through its normal build() path.
• Added CLI coverage showing aws_ec2_metadata is skipped during --no-environment validation.
• Ran cargo test --test integration --features cli-tests validate_no_environment_ -- --nocapture
• Ran make fmt
• Ran make check-clippy
• Ran ./scripts/check_changelog_fragments.sh

Change Type

• Bug fix
• New feature
• Dependencies
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

• Closes: Validate no-environment should perform transform/filter VRL checks #15037
• Related: aws_ec2_metadata performs network initialization in build() #25162

Notes

• aws_ec2_metadata remains a targeted exception because its build() currently performs network initialization.
• This PR adds changelog.d/15037_validate_no_environment_vrl.fix.md.