perf: set panic=abort and drop backtrace features (#342)

Reduces binary size of the updater staticlib when linked into the
Flutter engine. On host macOS arm64 the dylib shrinks from 3.07 MB
to 2.56 MB; the biggest iOS savings come from dropping the DWARF
unwind tables (__eh_frame, __gcc_except_tab, __unwind_info) that
panic=unwind generates.

- panic = "abort" in [profile.release]: kills unwind-table generation
  and eliminates dead panic-unwinding code paths. We don't use
  catch_unwind anywhere in the library. log-panics still runs its
  panic hook before abort, so panic messages continue to surface to
  logcat/oslog during development.
- Drop `backtrace` feature from anyhow and `with-backtrace` from
  log-panics: removes gimli + addr2line + rustc_demangle (~65 KB of
  symbolication machinery) that customers can't read anyway. A
  future in-engine crash reporter will symbolize native stacks,
  making these features redundant.

Cargo.lock

@@ -2,15 +2,6 @@
 # It is not intended for manual editing.
 version = 4
 
-[[package]]
-name = "addr2line"
-version = "0.25.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1b5d307320b3181d6d7954e663bd7c774a838b8220fe0593c86d9fb09f498b4b"
-dependencies = [
- "gimli",
-]
-
 [[package]]
 name = "adler2"
 version = "2.0.1"
@@ -121,21 +112,6 @@ version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c08606f8c3cbf4ce6ec8e28fb0014a2c086708fe954eaa885384a6165172e7e8"
 
-[[package]]
-name = "backtrace"
-version = "0.3.76"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bb531853791a215d7c62a30daf0dde835f381ab5de4589cfe7c649d2cbe92bd6"
-dependencies = [
- "addr2line",
- "cfg-if",
- "libc",
- "miniz_oxide",
- "object",
- "rustc-demangle",
- "windows-link",
-]
-
 [[package]]
 name = "base64"
 version = "0.22.1"
@@ -638,12 +614,6 @@ dependencies = [
  "wasip3",
 ]
 
-[[package]]
-name = "gimli"
-version = "0.32.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e629b9b98ef3dd8afe6ca2bd0f89306cec16d43d907889945bc5d6687f2f13c7"
-
 [[package]]
 name = "h2"
 version = "0.4.13"
@@ -994,7 +964,6 @@ version = "2.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "68f9dd8546191c1850ecf67d22f5ff00a935b890d0e84713159a55495cc2ac5f"
 dependencies = [
- "backtrace",
  "log",
 ]
 
@@ -1106,15 +1075,6 @@ dependencies = [
  "libc",
 ]
 
-[[package]]
-name = "object"
-version = "0.37.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ff76201f031d8863c38aa7f905eca4f53abbfa15f609db4277d44cd8938f33fe"
-dependencies = [
- "memchr",
-]
-
 [[package]]
 name = "once_cell"
 version = "1.21.4"
@@ -1390,12 +1350,6 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
-[[package]]
-name = "rustc-demangle"
-version = "0.1.27"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b50b8869d9fc858ce7266cce0194bd74df58b9d0e3f6df3a9fc8eb470d95c09d"
-
 [[package]]
 name = "rustix"
 version = "1.1.4"