ugh, i'm suddenly hitting this after running `cargo update` on my firmware project:
```
error[E0554]: `#![feature]` may not be used on the stable release channel
   --> ...\.cargo\registry\src\index.crates.io-1949cf8c6b5b557f\thiserror-2.0.12\src\lib.rs:268:42
    |
268 | #![cfg_attr(error_generic_member_access, feature(error_generic_member_access))]
```

this is what it updated (almost all of those are transient dependencies):
```
$ cargo update
    Updating crates.io index
     Locking 29 packages to latest Rust 1.88.0 compatible versions
    Updating autocfg v1.4.0 -> v1.5.0
    Updating bitflags v2.9.0 -> v2.9.1
    Updating bytemuck v1.23.0 -> v1.23.1
    Updating cfg-if v1.0.0 -> v1.0.1
    Updating cobs v0.2.3 -> v0.3.0
    Updating crunchy v0.2.3 -> v0.2.4
    Updating hashbrown v0.15.3 -> v0.15.4
    Updating indexmap v2.9.0 -> v2.10.0
    Updating lalrpop v0.22.1 -> v0.22.2
    Updating lalrpop-util v0.22.1 -> v0.22.2
    Updating libc v0.2.172 -> v0.2.174
    Updating lock_api v0.4.12 -> v0.4.13
    Updating memchr v2.7.4 -> v2.7.5
    Updating num_enum v0.7.3 -> v0.7.4
    Updating num_enum_derive v0.7.3 -> v0.7.4
    Updating parking_lot v0.12.3 -> v0.12.4
    Updating parking_lot_core v0.9.10 -> v0.9.11
    Updating portable-atomic v1.11.0 -> v1.11.1
    Updating postcard v1.1.1 -> v1.1.2
    Updating postcard-rpc v0.11.9 -> v0.11.10
    Updating postcard-schema v0.2.1 -> v0.2.2
    Updating redox_syscall v0.5.12 -> v0.5.13
    Updating rgb v0.8.50 -> v0.8.51
    Updating rustversion v1.0.20 -> v1.0.21
    Updating smallvec v1.15.0 -> v1.15.1
    Updating static_cell v2.1.0 -> v2.1.1
    Updating syn v2.0.101 -> v2.0.104
    Updating zerocopy v0.8.25 -> v0.8.26
    Updating zerocopy-derive v0.8.25 -> v0.8.26
```

has anyone else encountered this?

from the tree this might be pulled in by `cobs` (since it updated to v0.3 while `defmt-parser` didn't change), though i don't see what would cause it in the `Cargo.toml` there:
```
thiserror v2.0.12
└── cobs v0.3.0
[...]

thiserror v2.0.12
└── defmt-parser v1.0.0
[...]
```