fix: hide internal rest param from prefixed middleware

[raashish1601]

Fixes #233.

Summary

• prevent the generated {/*rest} wildcard used for prefixed router middleware from being copied into ctx.params
• keep prefix params available to both middleware and route handlers
• add a regression test for a parameterized prefix with global middleware and a child route

Validation

• npm run ts:check
• npm run ts:check:test
• npm run lint
• npm run build
• npm run format:check
• git diff --check
• $env:TS_NODE_PROJECT='tsconfig.ts-node.json'; node --require ts-node/register --test --test-name-pattern "does not expose internal rest param" test/router.test.ts
• $env:TS_NODE_PROJECT='tsconfig.ts-node.json'; node --require ts-node/register --test --test-name-pattern "Router#prefix" test/router.test.ts
• $env:TS_NODE_PROJECT='tsconfig.ts-node.json'; node --require ts-node/register --test test/router.test.ts
• $env:TS_NODE_PROJECT='tsconfig.ts-node.json'; node --require ts-node/register --test test/layer.test.ts
• $env:TS_NODE_PROJECT='tsconfig.ts-node.json'; node --require ts-node/register --test test/utils/*.test.ts

npm run test:core / the pre-commit test:all command could not run directly on this Windows shell because the package scripts use POSIX-style TS_NODE_PROJECT=... environment assignment. Running the equivalent PowerShell commands above passed for the touched test areas; the full command additionally hit existing Windows shelling failures in test/index.test.ts after npm run build.