fix: main_recursion enable lint in no_std crates and fix broken tests

[WaterWhisperer]

fixes the main_recursion lint which was previously skipping all no_std crates. It also fixes existing UI tests that were "testing nothing" because they were either marked as //@check-pass while missing expected errors, or were being compiled as libraries (which have no entrypoints).

• Lint Change: Removed the has_no_std_attr check in MainRecursion. The is_entrypoint_fn utility is now robust enough to handle entrypoint detection correctly without this manual skip.
• Test Fixes:
  • Updated entrypoint_recursion.rs by adding a dummy main function to force the compiler to treat it as a binary crate, allowing #[rustc_main] to be recognized as an entrypoint.
  • Added no_std_main_recursion.rs to specifically verify the lint works in #![no_std] environments.

Fixes #11034

• Added passing UI tests (including committed .stderr file)
• cargo test passes locally
• Executed cargo dev update_lints
• Run cargo dev fmt

changelog: [main_recursion]: now works in no_std crates and fixed broken tests

[rustbot]

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