chore(docs): unify rustdoc style across pallet-subtensor

[mcjkula]

Description

Standardizes rustdoc comments across pallets/subtensor/src/ on one canonical convention.

Split into 7 commits:

1. e7ec631: strip decorative /// --- / /// === / banner lines
2. 82f7793: normalize section headings (# Args -> # Arguments, etc.)
3. 77ce515: replace Returns an error if: prose with named # Errors bullets
4. 3917853: normalize event / error bullets to * 'Name': desc.
5. b1d136d: convert /// NOTE: / WARNING: / TODO: admonitions to headings or //
6. c35f571: move inline arg bullets under a proper # Arguments section
7. e3abf8f: normalize argument / return bullets to * `name`: desc.

Verified locally: cargo clippy -p pallet-subtensor --all-targets -- -D warnings and cargo fmt --check.

Related Issue(s)

N/A

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Breaking Change

None. This change is confined to /// rustdoc comments and a small number of // developer comments inside pallets/subtensor/src/.

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have run ./scripts/fix_rust.sh to ensure my code is formatted and linted correctly
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Screenshots (if applicable)

N/A - documentation-only change, no UI surface.

Additional Notes

Commit 77ce515 is the only one that adds new information (error-name enumerations in 5 extrinsics). Every name was cross-checked against the real Error::<T>::* call sites. All other commits are just reformatting.