refactor: enable extended clippy lint set

[farazdagi]

Summary

• Enable additional clippy lints workspace-wide (correctness, style, and clarity categories)
• Fix all existing violations across the codebase, one lint per commit for easy review

Lints enabled

# Correctness & safety
await_holding_lock = "deny"
unused_async = "deny"
large_futures = "deny"

# Style & clarity
cloned_instead_of_copied = "warn"
copy_iterator = "warn"
dbg_macro = "warn"
enum_glob_use = "warn"
explicit_into_iter_loop = "warn"
explicit_iter_loop = "warn"
flat_map_option = "warn"
implicit_clone = "warn"
map_flatten = "warn"
manual_let_else = "warn"
manual_ok_or = "warn"
manual_async_fn = "warn"
map_unwrap_or = "warn"
match_same_arms = "warn"
redundant_closure = "warn"
redundant_closure_call = "warn"
redundant_closure_for_method_calls = "warn"
redundant_else = "warn"
redundant_clone = "warn"
redundant_field_names = "warn"
redundant_test_prefix = "warn"
semicolon_if_nothing_returned = "warn"
todo = "warn"
uninlined_format_args = "warn"
unnested_or_patterns = "warn"

[coveralls]

Coverage is 78.38% — refactor/clippy-lints into main. No base build found for main.