The crate produce very big binary size

Just wanted to report that in a downstream lib elements-miniscript is the biggest contributor in binary size, maybe because it uses a lot of generics:

```shell
$ cargo bloat --release --crates
File .text Size Crate
9.6% 29.9% 1.9MiB elements_miniscript
6.7% 21.0% 1.3MiB wollet
4.2% 12.9% 833.4KiB std
1.9% 6.0% 388.4KiB elements
1.8% 5.7% 365.4KiB serde_cbor
1.6% 5.1% 328.8KiB [Unknown]
1.3% 4.1% 266.4KiB rustls
0.9% 2.9% 185.3KiB ring
0.7% 2.1% 138.5KiB electrum_client
0.4% 1.2% 78.0KiB simplicity
0.3% 1.0% 65.9KiB serde_json
0.3% 1.0% 64.2KiB bitcoin_hashes
0.3% 0.8% 53.0KiB signer
0.2% 0.7% 43.7KiB bitcoin
0.1% 0.4% 26.9KiB uniffi_core
0.1% 0.4% 26.1KiB secp256k1_sys
0.1% 0.4% 25.0KiB miniscript
0.1% 0.4% 24.7KiB ks_bindings
0.1% 0.3% 19.3KiB secp256k1_zkp_sys
0.1% 0.3% 17.2KiB bip39
0.6% 2.0% 129.8KiB And 41 more crates. Use -n N to show more.
32.2% 100.0% 6.3MiB .text section size, the file size is 19.6MiB
```

```shell
$ cargo bloat --release -n 10
File .text Size Crate Name
0.2% 0.7% 45.6KiB elements_miniscript elements_miniscript::miniscript::decode::parse
0.2% 0.7% 44.7KiB elements_miniscript elements_miniscript::miniscript::decode::parse
0.2% 0.7% 44.7KiB elements_miniscript elements_miniscript::miniscript::decode::parse
0.2% 0.7% 44.2KiB elements_miniscript elements_miniscript::miniscript::decode::parse
0.2% 0.7% 43.2KiB elements_miniscript elements_miniscript::miniscript::decode::parse
0.2% 0.7% 43.2KiB elements_miniscript elements_miniscript::miniscript::decode::parse
0.2% 0.7% 42.7KiB elements_miniscript elements_miniscript::miniscript::decode::parse
0.2% 0.5% 32.4KiB wollet wollet::clients::BlockchainBackend::full_scan
0.2% 0.5% 32.2KiB elements_miniscript elements_miniscript::descriptor::csfs_cov::cov::Le...
0.1% 0.4% 22.9KiB elements

No source files or tests are named. Reproduce the release build measurements with cargo bloat --release --crates and cargo bloat --release -n 10, then inspect the repeated elements_miniscript::miniscript::decode::parse entries and the descriptor::csfs_cov::cov entry. The issue does not define a target size or acceptance test, so the desired reduction must be clarified.

Scritto dal modello di indicizzazione a partire dal testo della issue.