MILAB-6960: move to workflow-tengo 6.10.5

[DenKoren]

Bumps the @platforma-sdk/workflow-tengo catalog entry to 6.10.5. Catalog + lockfile + changeset only — no workflow source changes.

What the bump picks up (superset; a block already past some of these skips them):

• 6.10.1 — pframes-rs 1.1.60: wide tables with hundreds of same-axis columns no longer overflow the engine thread stack.
• 6.10.2 — a python run environment now records its dependency specs before being saved, so its content hash reflects them. Two environments built from one interpreter stop deduplicating into each other, which could hand a script another package's venv.
• 6.10.3 / 6.10.4 — ptabler 2.1.11 / pframes-rs 1.1.61. The Linux pframes-rs-node addon drops its debug info: 208 MB → ~28 MB download. The TMPDIR compatibility layer for pre-contract backends now also works on Windows.
• 6.10.5 — pl-tengo imports replaces the clean-imports shell script. Unused-import detection moves into the builder's own parser, so it understands comments, respects word boundaries, and covers the tengo standard library too.

Verification

pnpm build:dev-no-software — all tasks green, including the tengo build and every check task (tsc, oxlint, oxfmt).

The lockfile diff carries a little churn beyond workflow-tengo (peer-graph reshuffles under caret-ranged dev dependencies). That drift is pre-existing — a plain pnpm install on main produces it too — and is not caused by this bump.

Part of a sweep applying the same bump across blocks.

Also in this PR: toolchain bump

CI's preflight (require-latest) gate demands the newest build toolchain, and this repo was behind it, so the same branch also moves:

• @platforma-sdk/block-tools → 2.16.0
• @platforma-sdk/tengo-builder → 4.1.0

Both are build-time only and carry no block behaviour. Re-verified with pnpm build:dev-no-software after the bump — all tasks green, the new tengo unused-import check included.