✨ Add RLP decoding to LibRLP (issue #1449)

[BhariGowda]

Closes #1449

Adds the decode side to LibRLP:

New API

Structs

• Item zero-copy view into encoded RLP input (offset + length + type)

Public decoders

• decodeBytes(bytes memory) → bytes memory
• decodeUint256(bytes memory) → uint256
• decodeAddress(bytes memory) → address
• decodeBytes32(bytes memory) → bytes32
• decodeList(bytes memory) → Item[] memory

Item overloads

• decodeBytes(Item), decodeUint256(Item), decodeAddress(Item), decodeBytes32(Item)

Iteration

• next(Item) next sibling, empty sentinel when exhausted
• isList(Item) → bool
• isEmpty(Item) → bool

Design

• Pure assembly, zero-copy list views into input
• _decodeLength: single shared prefix decoder with full validation
• Permissive (accepts non-canonical leading-zero scalars, like OZ reference)
• mcopy avoided (paris EVM); word-copy loop with tail zeroization

Tests

42 tests passing fuzz + edge cases + 9 revert cases + round-trips

[github-actions]

Gas Snapshot Comparison Report

Generated at commit : 5ea73fa, Compared to commit : ab96a83

Contract Name	Test Name	Main Gas	PR Gas	Diff
LibRLPTest	testComputeAddressForLargeNonces()	1750	1772	22
	testComputeAddressOriginalForLargeNonces()	3495	3517	22
	testComputeAddressOriginalForSmallNonces()	2088	2111	23
	testRLPEncodeBytes()	250147	250198	51
	testRLPEncodeBytes2()	155904	156672	768
	testRLPEncodeList()	3426655	718111	-2708544
	testRLPEncodeList2()	808242	793155	-15087
	testRLPEncodeListEdgeCases()	1807977	1819406	11429
	testRLPEncodeStringEdgeCases()	20538	20560	22
	testRLPEncodeUint()	1461629	1317882	-143747
	testRLPPUint256()	363834	363866	32
	test__codesize()	18246	26050	7804
	testRLPDecodeAddressSingleByte()	-	2624	-
	testRLPDecodeBytes32()	-	2728	-
	testRLPDecodeBytesEdgeCases()	-	25047	-
	testRLPDecodeEmptyItemQueries()	-	672	-
	testRLPDecodeEmptyList()	-	1126	-
	testRLPDecodeInvalidReverts()	-	41994	-
	testRLPDecodeKnownVectors()	-	9552	-
	testRLPDecodeListIteratorEquivalence()	-	8109	-
	testRLPDecodeListKnownVector()	-	4602	-
	testRLPDecodeLongListRoundTrip()	-	38483	-
	testRLPDecodeNestedList()	-	10084	-
	testRLPDecodeNonCanonical()	-	2514	-
	testRLPDecodeUint()	-	66339	-
LibRLPWithCLZTest	testComputeAddressForLargeNonces()	1750	-	-
	testComputeAddressForSmallNonces()	997	-	-
	testComputeAddressOriginalForLargeNonces()	3495	-	-
	testComputeAddressOriginalForSmallNonces()	2088	-	-
	testRLPEncodeBytes()	250090	-	-
	testRLPEncodeBytes2()	155904	-	-
	testRLPEncodeList()	735942	-	-
	testRLPEncodeList2()	810708	-	-
	testRLPEncodeListEdgeCases()	1807743	-	-
	testRLPEncodeStringEdgeCases()	20424	-	-
	testRLPEncodeUint()	1175570	-	-
	testRLPPUint256()	363834	-	-
	test__codesize()	18292	-	-