Extract env/process/clock i64 lowering into host_env_proc_clock.rs (#1254)

[daedalus-omt]

Summary

Seventeenth cranelift_backend.rs split under #1254. Extracted the env/process/clock i64-lowering closure from the parent monolith into host_env_proc_clock.rs.

Scope

Pure function move — no struct/static relocation (like host_net_http, PR #1381). 17 functions moved:

• env_option_match helpers (~line 4527): lower_i64_env_option_match_stmt + 4 helpers
• env_option_call (~line 8024): lower_i64_env_option_call_let_stmts
• env_match_value/some_arm/len/get_key (~lines 10518–10632): 4 functions
• clock/process intrinsics + audited helpers (~lines 15468–15704): 7 functions

Siblings Decision (grep rule per #1382 recipe)

• Stay in parent: SpikeEnv, I64StaticBindings, i64_known_static_env, lower_i64_string_option_len_call_let_stmts — callers cross slice boundaries; moved fns reach via use super::*.
• No private_interfaces fix required

Lines

File	Before	After	Delta
cranelift_backend.rs	20,914	20,338	-576
host_env_proc_clock.rs	—	586	+586

Ratchet Ceilings Updated

Tracked item	Old	New
summary.top_file_line_share	0.7466	0.7401
summary.top_file_lines	67,390	66,814
cranelift_backend.rs	20,914	20,338
(new) host_env_proc_clock.rs	—	586

Validation

• cargo build -p axiomc — clean (no errors)
• cargo test -p axiomc --lib — 688 passed, 5 failed (same pre-existing env-dependent failures on main: wasm alias build, proof-workload http example, socket-binding stdlib-http tests)
• plan doc ratchet check — passes

Governance

• Follows Document the host-capability slice recipe for pickup #1382 recipe. Do not run cargo fmt on backend files. All moved fns pub(crate).

Refs #1254.

[athena-omt]

Athena review: APPROVE

Reviewed on the Athena node (OMT-NAS) at head 0813beaf72d5aac463217f868ffb9e25d176239b, which matches the PR head and is not behind main (HEAD..origin/main = 0).

This PR extracts the env/process/clock i64 lowering helpers out of cranelift_backend.rs into a new sibling module cranelift_backend/host_env_proc_clock.rs, continuing the decomposition pattern already used by host_crypto.rs, host_fs.rs, and host_net_http.rs.

Findings:

• Wiring is correct. mod host_env_proc_clock; + pub(crate) use host_env_proc_clock::*; were added next to the sibling module declarations. The new module uses use super::* and re-exports its pub(crate) helpers, so existing call sites in cranelift_backend.rs continue to resolve.
• No orphaned or duplicate definitions. The fn definitions removed from cranelift_backend.rs (env/process/clock, e.g. lower_i64_env_option_match_stmt, i64_env_option_*, lower_i64_clock_intrinsic_expr, lower_i64_process_intrinsic_expr) now live exactly once in the new module; grep confirms zero leftover defs and a clean compile (all checks green).
• Docs updated coherently. docs/compiler-source-decomposition-plan.md reflects the reduced cranelift_backend.rs line count (20914 → 20338) and the new module's 586 lines.
• Branch is current with main. No rebase/update is required, so no post-update CI wait was needed.
• All 7 status checks are green and auto-merge (squash) is enabled.

This is a behavior-preserving refactor with no substantive blockers. Approving.