ci: concurrency + timeout-minutes on 3 queue-saturating workflows (#248)

Same pattern as proven#115. Targets the 3 workflows on this repo lacking
\`concurrency:\` (rust-ci, boj-build, instant-sync). Reduces queue
pressure against the GitHub Pro 40-job concurrent ceiling.

Other workflows on this repo (abi-verify, codeql, coq-build,
scorecard-enforcer, hypatia-scan, secret-scanner) already had
concurrency declarations.

Note: uncommitted parallel-session changes in formal/ are NOT included
in this PR (per estate parallel-session git defence).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/boj-build.yml

@@ -4,9 +4,13 @@ on:
   push:
     branches: [main, master]
   workflow_dispatch:
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 jobs:
   trigger-boj:
     runs-on: ubuntu-latest
+    timeout-minutes: 5
     steps:
       - name: Checkout
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2

.github/workflows/instant-sync.yml

@@ -11,9 +11,14 @@ on:
 permissions:
   contents: read
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   dispatch:
     runs-on: ubuntu-latest
+    timeout-minutes: 5
     steps:
       - name: Trigger Propagation
         uses: peter-evans/repository-dispatch@28959ce8df70de7be546dd1250a005dd32156697 # v3

.github/workflows/rust-ci.yml

@@ -12,13 +12,18 @@ on:
 permissions:
   contents: read
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   rust-ci:
     uses: hyperpolymath/standards/.github/workflows/rust-ci-reusable.yml@cc5a372af1af1b202c17f1b21efd954e6c038bef
 
   no-default-features:
     name: Cargo build + test (ephapax-cli, --no-default-features)
     runs-on: ubuntu-latest
+    timeout-minutes: 20
     if: hashFiles('Cargo.toml') != ''
 
     # Proves ephapax can be built and tested with zero git dep on the