feat: Support loading environment variables from a file

[dsarlis]

Add support to load environment variables from a file.

Some canisters might expect that certain environment variables are set when calling certain endpoints, so with this change we make it easier to have such canisters be benchmarked without the need to disable any environment variable related logic and write benchmarks with minimal code instrumentation as usual.

The idea is very similar to how stable memory can be instantiated from a file, essentially exposing another option in canbench.yml to support environment variables in a similar fashion. The format of the file is CSV which feels natural for a list of key, value pairs like environment variables.

[github-actions]

canbench 🏋 (dir: ./examples/btreemap_vs_hashmap) f7cc166 2026-05-15 07:35:07 UTC

✅ ./examples/btreemap_vs_hashmap/canbench_results.yml is up to date
📦 canbench_results_btreemap-vs-hashmap-example.csv available in artifacts

---------------------------------------------------

Summary:
  instructions:
    status:   No significant changes 👍
    counts:   [total 3 | regressed 0 | improved 0 | new 0 | unchanged 3]
    change:   [max 0 | p75 0 | median 0 | p25 0 | min 0]
    change %: [max 0.00% | p75 0.00% | median 0.00% | p25 0.00% | min 0.00%]

  heap_increase:
    status:   No significant changes 👍
    counts:   [total 3 | regressed 0 | improved 0 | new 0 | unchanged 3]
    change:   [max 0 | p75 0 | median 0 | p25 0 | min 0]
    change %: [max 0.00% | p75 0.00% | median 0.00% | p25 0.00% | min 0.00%]

  stable_memory_increase:
    status:   No significant changes 👍
    counts:   [total 3 | regressed 0 | improved 0 | new 0 | unchanged 3]
    change:   [max 0 | p75 0 | median 0 | p25 0 | min 0]
    change %: [max 0.00% | p75 0.00% | median 0.00% | p25 0.00% | min 0.00%]

---------------------------------------------------
CSV results saved to canbench_results.csv

[github-actions]

canbench 🏋 (dir: ./examples/fibonacci) f7cc166 2026-05-15 07:35:11 UTC

✅ ./examples/fibonacci/canbench_results.yml is up to date
📦 canbench_results_fibonacci-example.csv available in artifacts

---------------------------------------------------

Summary:
  instructions:
    status:   No significant changes 👍
    counts:   [total 5 | regressed 0 | improved 0 | new 0 | unchanged 5]
    change:   [max 0 | p75 0 | median 0 | p25 0 | min 0]
    change %: [max 0.00% | p75 0.00% | median 0.00% | p25 0.00% | min 0.00%]

  heap_increase:
    status:   No significant changes 👍
    counts:   [total 5 | regressed 0 | improved 0 | new 0 | unchanged 5]
    change:   [max 0 | p75 0 | median 0 | p25 0 | min 0]
    change %: [max 0.00% | p75 0.00% | median 0.00% | p25 0.00% | min 0.00%]

  stable_memory_increase:
    status:   No significant changes 👍
    counts:   [total 5 | regressed 0 | improved 0 | new 0 | unchanged 5]
    change:   [max 0 | p75 0 | median 0 | p25 0 | min 0]
    change %: [max 0.00% | p75 0.00% | median 0.00% | p25 0.00% | min 0.00%]

---------------------------------------------------
CSV results saved to canbench_results.csv

[Copilot]

Pull request overview

Adds support in canbench for preloading canister environment variables from a user-provided file, enabling benchmarking of canisters that depend on ic_cdk::api::env_var_value(...) without additional instrumentation.

Changes:

• Extends canbench.yml parsing to accept an env_vars.file path and threads it through benchmark execution.
• Creates canisters in PocketIC with CanisterSettings.environment_variables populated from the file.
• Adds new test canisters + CLI tests covering success, missing file, and invalid file cases, plus updates crate docs.

Reviewed changes

Copilot reviewed 14 out of 15 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/environment_variables/src/main.rs	New test canister that reads env vars at init and asserts expected values in a benchmark.
tests/environment_variables/environment_variables.csv	Sample env var data file used by the test canister.
tests/environment_variables/canbench.yml	Test config exercising env_vars.file.
tests/environment_variables_invalid/src/main.rs	Minimal canister for invalid env var file test.
tests/environment_variables_invalid/environment_variables_invalid.csv	Invalid env var file fixture (no comma separator).
tests/environment_variables_invalid/canbench.yml	Test config pointing at invalid env var file.
tests/environment_variables_file_does_not_exist/src/main.rs	Minimal canister for missing env var file test.
tests/environment_variables_file_does_not_exist/canbench.yml	Test config pointing at a non-existent env var file.
tests/Cargo.toml	Registers the new test canister binaries.
Cargo.lock	Locks new dependency additions.
canbench-rs/src/lib.rs	Documents environment-variable file support in the crate-level docs.
canbench-bin/tests/tests.rs	Adds integration tests for env var loading / error output.
canbench-bin/src/main.rs	Adds env_vars to config parsing and passes the path into run_benchmarks.
canbench-bin/src/lib.rs	Implements env var file parsing and applies it via CanisterSettings during canister creation.
canbench-bin/Cargo.toml	Adds ic-management-canister-types dependency for EnvironmentVariable.

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[dsarlis]

@mraszyk Feel free to merge when ready.