fix(process): share Node dotenv parsing for loadEnvFile

[andrewtdiz]

Summary

• shares the Node-compatible dotenv parser behind util.parseEnv with process.loadEnvFile
• matches Node dotenv cases for export prefixes, inline # comments, multiline quoted/backtick values, duplicate keys, and unterminated quotes
• updates process.loadEnvFile path handling for omitted/undefined/null defaults, strings, Buffers, file URLs, non-file URL errors, and invalid path argument errors
• expands parity coverage for both util.parseEnv and process.loadEnvFile

Batching rationale

These issues share the same behavioral surface: process.loadEnvFile should parse .env contents using the same Node dotenv rules exposed by util.parseEnv, and path validation needed to pass the raw JS value through lowering/codegen to runtime. Keeping them together avoids landing parser behavior that the process loader cannot yet use.

Tests

• RUSTC_WRAPPER= cargo test -p perry-runtime util_parse_env
• RUSTC_WRAPPER= cargo check -p perry-runtime -p perry-hir -p perry-codegen -p perry
• cargo fmt --all -- --check
• git diff --check
• ./scripts/check_file_size.sh
• jq empty test-parity/known_failures.json
• PATH=/home/github-runner/actions-runner/externals/node24/bin:$PATH ./run_parity_tests.sh --suite node-suite --module util --filter parse-env
• PATH=/home/github-runner/actions-runner/externals/node24/bin:$PATH ./run_parity_tests.sh --suite node-suite --module process/methods --filter load-env-file
• PATH=/home/github-runner/actions-runner/externals/node24/bin:$PATH ./run_parity_tests.sh --suite node-suite --module process/methods
• PATH=/home/github-runner/actions-runner/externals/node24/bin:$PATH ./run_parity_tests.sh --suite node-suite --module util (68 pass, 1 unrelated existing node-suite/util/get-system-error output mismatch)

Non-goals

• does not implement npm dotenv package behavior or dotenv/config wrapper changes
• does not broaden process.env storage semantics beyond loaded values
• does not change other fs path-like URL validation

Closes #3423. Closes #2985. Closes #3045.

[andrewtdiz]

Refreshed this branch for the latest mainline changes.

• Merged current origin/main, including the util/sys manifest mirror fix that was failing cargo-test.
• Applied the ReflectIsExtensible stable-hash tag correction required while current mainline still has the duplicate tag.
• Regenerated the API manifest docs; they were already current after the merge.
• Local checks passed: CARGO_TARGET_DIR=/root/perry/target cargo test -p perry-api-manifest sys_alias_mirrors_util_manifest, CARGO_TARGET_DIR=/root/perry/target cargo test -p perry-hir stable_hash::tests::expr_variant_stable_hash_tags_are_unique, CARGO_TARGET_DIR=/root/perry/target cargo test -p perry-runtime util_parse_env::tests::parses_node_compatible, cargo fmt --all -- --check, git diff --check against the branch merge-base, git diff --check, scripts/check_file_size.sh, and workflow YAML parsing.