A recent fix [1] in the picky-asn1-der crate highlights an issue that
could lead to faulty results handed off by the abstractions in the
tss-esapi crate. Specifically, mishandling of ASN.1 Integers could
result in invalid encodings of various pieces of data such as elliptic
curve points.

[1] https://github.com/Devolutions/picky-rs/pull/209/files

Signed-off-by: Ionut Mihalcea <ionut.mihalcea@arm.com>

Bumping MSRV to 1.60.0 as required for the picky-asn1 crate.

Also setting the MSRV for clippy and fixing some of the remaining
warnings. Some of the things clippy complains about for newer versions
of the compiler can be fixed/changed without losing support for older
compiler versions, but some features are incompatible. Since clippy is
now configured to understand the MSRV, there's also no need for some of
the `allow` attributes.

Signed-off-by: Ionut Mihalcea <ionut.mihalcea@arm.com>