Update syn requirement from 1.0.107 to 2.0.48 (#881)

* Update syn requirement from 1.0.107 to 2.0.48

Updates the requirements on [syn](https://github.com/dtolnay/syn) to permit the latest version.
- [Release notes](https://github.com/dtolnay/syn/releases)
- [Commits](https://github.com/dtolnay/syn/compare/1.0.107...2.0.48)

---
updated-dependencies:
- dependency-name: syn
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

* rtic-macros: attr.path -> attr.path()

* rtic-macros: tokens -> parse_args()

Fix parsing of InitArgs, IdleArgs, *Args

Including HardwareTaskArgs, SoftwareTaskArgs

* rtic-macros: Rename content to input

As syn2 removes the surrounding parenthesis as
part of parse_args() the distinction between
input and content is redundant

* rtic-macros: Handle removal of Expr::Type

Manually parse local_resources

With type ascription de-RFCd syn2 dropped
Expr::Type

* rtic-macros: Syn upgrade CHANGELOG

* rtic-macro: Retain most old errors as they were

Spans are not equal, but good enough

* rtic-macros: syn2 changed some error messages

Additionally some spans were not retained
with the manual parsing workaround

* rtic-macros: clippy fixes

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Henrik Tjäder <henrik@tjaders.com>

rtic-macros/CHANGELOG.md

@@ -11,6 +11,10 @@ For each category, *Added*, *Changed*, *Fixed* add new entries at the top!
 
 - Unstable ESP32-C3 support.
 
+### Changed
+
+- Upgraded from syn 1.x to syn 2.x
+
 ## [v2.0.1] - 2023-07-25
 
 ### Added