Update zcash_primitives to orchard 0.3; release zcash_primitives and zcash_proofs 0.8.

[ebfull]

• This updates the zcash_primitives crate to use orchard 0.3 which is a breaking change; we do a release of zcash_primitives 0.8.
• We update zcash_proofs to use zcash_primitives 0.8 which is a breaking change; we do a release of zcash_proofs 0.8.
• We update zcash_extensions, zcash_client_backend, zcash_client_sqlite to use zcash_primitives 0.8 which is a breaking change; we are not releasing these crates in this PR.
• We also update zcash_client_backend to use orchard 0.3.

[nuttycom]

utACK of the first commit; I authored the second (albeit mechanically, using clippy +beta --fix) so it should be independently checked.

[codecov]

Codecov Report

Base: 74.00% // Head: 73.30% // Decreases project coverage by -0.69% ⚠️

Coverage data is based on head (5bf3698) compared to base (49bdd86).
Patch coverage: 50.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #681      +/-   ##
==========================================
- Coverage   74.00%   73.30%   -0.70%     
==========================================
  Files         104      106       +2     
  Lines       10081    10748     +667     
==========================================
+ Hits         7460     7879     +419     
- Misses       2621     2869     +248     

Impacted Files	Coverage Δ
zcash_client_backend/src/keys.rs	88.55% <ø> (ø)
zcash_client_sqlite/src/wallet/init.rs	70.90% <ø> (ø)
.../src/transaction/components/transparent/builder.rs	47.82% <0.00%> (ø)
zcash_proofs/src/sprout.rs	0.00% <0.00%> (ø)
zcash_proofs/src/lib.rs	36.00% <50.00%> (ø)
zcash_client_sqlite/src/prepared.rs	84.51% <100.00%> (ø)
zcash_primitives/src/legacy.rs	98.03% <100.00%> (ø)
zcash_primitives/src/transaction/util/sha256d.rs	90.00% <100.00%> (ø)
zcash_primitives/src/sapling/redjubjub.rs	90.32% <0.00%> (-1.08%)	⬇️
zcash_proofs/src/circuit/ecc.rs	98.28% <0.00%> (-0.35%)	⬇️
... and 5 more

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[daira]

Post-hoc ACK