buffer: switch to memmap2, destroy shm pools, never underflow refcounts

memmap 0.7 is unmaintained (RUSTSEC-2020-0077); memmap2 is a drop-in
replacement. Drop the unused shlex dependency.

Each resize created a new wl_shm_pool that was never destroyed; keep the
pool on the buffer and destroy it with it. A wl_buffer.release for a
buffer we didn't consider acquired used to underflow refcnt and wedge
rendering. Fix the lifetime-elision warnings while here.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Cargo.lock

@@ -462,16 +462,6 @@ version = "2.7.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "523dc4f511e55ab87b694dc30d0f820d60906ef06413f93d4d7a1385599cc149"
 
-[[package]]
-name = "memmap"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6585fd95e7bb50d6cc31e20d4cf9afb4e2ba16c5846fc76793f11218da9c475b"
-dependencies = [
- "libc",
- "winapi",
-]
-
 [[package]]
 name = "memmap2"
 version = "0.9.5"
@@ -809,12 +799,6 @@ dependencies = [
  "digest",
 ]
 
-[[package]]
-name = "shlex"
-version = "1.3.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0fda2ff0d084019ba4d7c6f371c95d8fd75ce3524c3cb8fb653a3023f6323e64"
-
 [[package]]
 name = "simd-json"
 version = "0.13.8"
@@ -1289,13 +1273,12 @@ dependencies = [
  "fontconfig",
  "fuzzy-matcher",
  "libpulse-binding",
- "memmap",
+ "memmap2",
  "nix 0.26.4",
  "rcalc_lib",
  "rusttype",
  "serde",
  "serde_yaml",
- "shlex",
  "simd-json",
  "unicode-segmentation",
  "walkdir",