fix(aop): advice/pointcut macros generate valid Rust + uppercase aliases

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Summary

Fixes the broken hiver-aop API that made it unusable from downstream crates.

• Fixes hiver-aop README/API example does not compile from downstream crates #60 — hiver-aop README/API example does not compile from downstream crates
• Fixes [Bug] https://crates.io/crates/hiver-aop 用不了 #61 — [Bug] https://crates.io/crates/hiver-aop 用不了

Root cause

The published 0.1.0-alpha.6 was unusable: every advice/pointcut macro emitted
impl #func_name { ... } where #func_name is a function, not a type. This
broke in every context:

• inside an impl Aspect { #[before] ... } block →
  error: implementation is not supported in traits or impls
• on a free #[before] fn free_advice() →
  error[E0573]: expected type, found function free_advice

Additionally, the runtime type re-export was previously gated behind
#[cfg(not(proc_macro))] (now removed), so hiver_aop::JoinPoint was not
reachable downstream, and the README used uppercase Spring-style macro names
(Aspect/Before/...) that were never exported.

The fix

The macros now emit the annotated fn unchanged plus a uniquely-named
companion const recording the pointcut expression and advice kind:

#[before("execution(* *..*.*(..))")]
fn log_before(&self, jp: &JoinPoint) { ... }
// expands to:
const _HIVER_BEFORE_LOG_BEFORE_META: (&'static str, &'static str) =
    ("execution(* *..*.*(..))", "before");

A bare const (not a nested impl) is valid Rust both at module scope and
inside an impl block, so advice now works in both contexts.

Changes

Area	Change
hiver-aop-macros/src/advice.rs	All 5 advice macros emit fn + companion const via a shared expand_advice helper; removed invalid impl #func_name
hiver-aop-macros/src/pointcut.rs	Same companion-const fix
hiver-aop/src/lib.rs	Re-export uppercase aliases (Aspect/Before/After/Around/AfterReturning/AfterThrowing/Pointcut) so the README import shape compiles
hiver-aop/README.md	Rewritten to the real, compiling API + a "Pointcut expressions in Rust" section (no JVM package semantics)
Doc comments	advice.rs/pointcut.rs/aspect.rs/runtime.rs/lib.rs examples updated to compile-ready shape
hiver-aop/tests/	New trybuild regression suite: free-fn advice (pass), impl-block advice (pass — the original failing case), uppercase aliases (pass), wrong-macro-name (compile_fail)
examples/logging_aspect.rs	Re-enabled (was .disabled) as a buildable, runnable example
hiver-aop-macros/README.md	New — Cargo.toml referenced ./README.md but it was missing, which blocked cargo package/publish

Verification

• Both exact reproductions from issue hiver-aop README/API example does not compile from downstream crates #60 now cargo check from a fresh
  downstream crate (uppercase aliases inside impl block, and lowercase free fn).
• cargo test -p hiver-aop -p hiver-aop-macros: 56 unit tests + 1 trybuild
  suite (4 cases) + 2 compiled doc-tests all pass.
• cargo run -p hiver-aop --example logging_aspect runs end-to-end.
• cargo +nightly fmt -p hiver-aop -p hiver-aop-macros -- --check: clean.
• cargo clippy introduces no new warnings (pre-existing unwrap_used warnings
  in untouched runtime.rs registry code are out of scope).

Note on releasing

This PR does not bump the version (per discussion). The fix lives in-repo;
shipping it to crates.io is a separate tag-triggered release.yml step. Note
that hiver-aop-macros must be published before hiver-aop (the latter
declares a version dependency on the former).

Out of scope

Dependabot PRs (#64/#65/#66) and the dependency-update issue #16 are unrelated
dependency bumps and are not addressed here.

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📦 Public API Changes

No public API changes.